The Construction And Performance Of Aluminum Batteries Based On Metal-organic Frameworks Quasi-Solid-state Electrolyte

With the proposal of the "carbon peaking and carbon neutrality" goals in China,the large-scale utilization of renewable energy and the development of energy storage technologies are becoming more and more important.Lithium-ion batteries,the dominator in the energy storage market,are increasingly expensive and face safety risks,which are difficult to meet the demand for large-scale energy storage in the future.Non-aqueous aluminum batteries of low cost and high safety are considered as one of ideal battery technology for large-scale energy storage due to the abundant natural resources of aluminum and the utilization of non-flammable ionic liquid(IL)electrolyte.However,the IL electrolyte suffers from poor air stability and dissolution of high-capacity positives electrode materials,leading to battery swelling and rapid capacity decay,which limits the practical application of non-aqueous aluminum batteries.In order to solve the above issues,herein the IL electrolyte is encapsulated into the metal-organic frameworks(MOF)to synthesize a quasi-solid-state electrolyte(IL@MOF)with high air stability and excellent ionic conductivity,and the quasi-solid-state aluminum-carbon batteries and aluminumsulfur batteries are constructed based on IL@MOF electrolyte.The reasons for the high air stability and the ion transport mechanism of IL@MOF electrolyte are investigated.The interface characteristics between IL@MOF electrolyte and positive/negative electrodes are studied,which is used to further analyze the mechanism of’ inhibiting battery swelling and improving the cycle life of the aluminum batteries by IL@MOF quasi-solid-state electrolyte.In addition,gel polymer electrolyte(GPE)is introduced into IL@MOF to synthesize a flexible quasi-solid-state electrolyte(IL@MOF-GPE),which can be preparate in large scale.The quasi-solid-state aluminum-carbon and aluminum-sulfur pouch cells are designed and manufactured based on IL@MOF-GPE electrolyte,which is proved that the quasi-solid-state aluminum-based pouch cells exhibit the performance comparable to that of the commercial batteries.The main research results of this paper are as follows:(1)The IL electrolyte is encapsulated in the channels of zirconium-based MOF nanoparticles to prepare a quasi-solid-state electrolyte(IL@MOF)with high air stability and excellent ionic conductivity.In IL@MOF electrolyte,IL provides active ions and MOF acts as an ion transport framework,and the ionic conductivity of IL@MOF can reach 7.5×10-4 S cm-1 at room temperature due to its open 3D pore and the "nanoscale" contact between IL@MOF particles.Moreover,the organic ligand in MOF repels H2O molecules,which lessens the influence of H2O in air on IL in MOF channels,so that IL@MOF electrolyte can still maintain the initial electrochemical activity after exposure in air for 2 hours,revealing high air stability.This design of quasi-solid-state electrolyte would provide an important basis for the construction of highly stable aluminum battery systems.(2)The quasi-solid-state aluminum-carbon batteries with high air stability and aluminum-sulfur batteries with long cycle life are constructed based on IL@MOF electrolyte.Due to the nano-particle morphology and open 3D nano-porous channels of MOF,IL@MOF electrolyte can form a uniform and stable "nanoscale"interface with positive and negative electrodes,achieving efficient interfacial transportation of AlCl4-ions.The as-assembled quasi-solid-state aluminum-carbon batteries can deliver a specific capacity of 70 mAh g-1 with graphite loading of 9 mg cm-2.At the same time,due to the protective effect of the MOF frameworks on the IL electrolyte in the channel,the quasi-solid aluminum-carbon battery can still work when directly exposed to air,exhibiting high air stability.In addition,the nano-porous channels of MOF in IL@MOF are filled with IL ions,which successfully inhibit the shuttle effect of soluble poly sulfides,improving the utilization of sulfur,so that the quasi-solid-state aluminum-sulfur batteries deliver a high specific capacity of 820 mAh g-1 in the first cycle and 78%capacity retention beyond 300 cycles,revealing long-term cycle life.The strategy of quasi-solid-state electrolyte solves the problem of swelling and short lifespan in aluminum batteries caused by poor air stability and dissolution of positive electrode in IL electrolyte.These works provide guidance for the design and manufacture of quasi-solid-state aluminum batteries with high stability.(3)The quasi-solid-state aluminum-based pouch cells with performance comparable to that of commercial batteries are designed and manufactured.20 wt%GPE is introduced into IL@MOF to synthesize a flexible IL@MOF-GPE quasisolid-state electrolyte which could he preparate in large scale,and hundred-mAh quasi-solid-state aluminum-carbon and aluminum-sulfur pouch cells are fabricated based on IL@MOF-GPE electrolyte.The aluminum-based pouch cells can run successfully and support the operation of electronic devices,which is attributed to the "flexible contact" interface between the IL@MOF-GPE electrolyte and the positive/negative electrode.Consequently,the quasi-solid-state aluminum-carbon pouch cell delivers a capacity of 105 mAh with a life of 450 cycles,and the capacity of the quasi-solid-state aluminum-sulfur pouch cell is 288 mAh with a life of 400 cycles.More importantly,the gravimetric energy density of quasi-solid-state aluminum-carbon and aluminum-sulfur pouch cells are 31 Wh Kg-1 and 110 Wh Kg-1,respectively,which can be comparable to that of the commercial lead-acid batteries,nickel-cadmium battery and nickel-metal hydride batteries.These works provide a demonstration for the application of aluminum batteries.