Design And Energy Storage Applications Of Electrode Materials For Aqueous Al-ion Batteries

Along with the continuous development of society and technology,the increasing consumption of fossil energy and emission of greenhouse gas have led to a global energy and environmental crisis,which has led to an urgent need for renewable energy.However,most of the new energy such as hydro,solar,wind,and geothermal energy are facing the problems of the uneven spatial and temporal distribution and poor grid distribution,which drives the demand for grid-scale energy storage devices.Therefore,it is urgent to develop new energy storage devices with high energy density,long cycling life and low cost.Among the current commercial energy storage devices,lithium-ion batteries（LIBs）with excellent energy density and cycling stability dominate in many fields.However,the limited lithium resources have led to the rising cost of lithium-ion batteries,while the safety of organic electrolytes has never been completely solved,and these problems have driven the development of new types of energy storage devices beyond lithium.Benefiting from electrode materials with ultra-high theoretical capacities,aluminum ion batteries（AIBs）can achieve extremely high theoretical energy densities,which has led to widespread interest in the field of energy storage.The low specific gravity of Al metals and their ability to carry three charges allow them to achieve very high capacities on both the anode and cathode.Moreover,Al metals are stable in aqueous solutions,which ensures that metal-based AIBs can operate in aqueous electrolytes that are inexpensive,safe,and have high ionic conductivity.These advantages make aqueous AIBs powerful candidates for next-generation energy storage devices.However,the formation of dense aluminum oxide layers on the surface of the Al anodes leads to passivation of the electrode,while the low Al deposition potential makes it difficult to avoid hydrogen evolution reaction（HER）,which limits the performance of Al-ion full batteries.In addition,the high charge density of Al³⁺makes the desolvation process more difficult and easily destroys the structure of the cathode materials.Traditional cathode materials such as vanadium-based oxides,manganese-based oxides,Prussian blue analogs,and quinone-based organics face low capacity,short cycle life,and poor rate performance when storing Al³⁺in aqueous electrolytes,which limit the actual energy storage capacity of AIBs.In order to solve these problems of AIBs,this paper designs a unique nanoarray structure to regulate the solid electrolyte interphase（SEI）structure and the transport process of Al³⁺,which effectively solves the problems of high transport resistance and short cycle life of Al anode.Meanwhile,the transition metal oxide（TMO）material with organic pre-insertion layers is designed to shield the strong polarization of Al³⁺and weaken the ion transport resistance.By modifying the anode and cathode,the assembled aqueous AIBs can achieve ultra-high energy density and superior cycling stability.The research in this paper includes the following aspects.1.Aluminum-copper alloy anode materials for high-energy aqueous aluminum batteriesThe extremely high theoretical capacity(2981 m Ah g^-1)and low cost of metallic Al give it the potential to be a high-performance anode material for aluminum ion batteries.However,severe passivation and side reaction problems make the Al ions stripping/plating process on the Al metal surface only poorly reversible,which limits the practical performance of Al foil anodes.Eutectic Al₈₂Cu₁₈(E-Al₈₂Cu₁₈)with ordered lamellar nanoarray electrodes consisting of alternatingα-Al and Al₂Cu intermetallic phases can be obtained by in situ eutectic solidification reaction,which can significantly enhance the reversibility of the aluminum anode.Among them,the ultra-thin arrays ensure that only self-limiting oxide layers are formed on the Al surface to isolate the electrolyte,the periodically localized galvanic couples of theα-Al and Al₂Cu phases paired with each other can provide sufficient driving force for the transport of Al ions through the oxide layer by the potential difference,and the Al₂Cu array can induce the reversible stripping/plating of Al ions.Benefiting from these advantages,the E-Al₈₂Cu₁₈ electrode achieves a highly reversible Al stripping/plating process over 2000 hours,exhibiting very low overpotential and high energy efficiency（EE）.When assembled as a full battery using an E-Al₈₂Cu₁₈ anode with a pre-inserted Al_xMn O₂ cathode,it is capable of delivering an energy density above 670 Wh kg^-1/815 Wh L^-1（based on the mass or volume of the Al_xMn O₂ cathode）,and its capacity can be maintained at more than 80%of initial capacity over 400 cycles.The cell-level energy density of this battery exceeds 90 Wh kg^-1 when evaluated using practical evaluation methods for Al battery technologies.2.Uniformly MXene-grafted eutectic aluminum-cerium alloys as flexible and reversible anode materials for rechargeable aluminum-ion batteryThe high content of intermetallic compounds significantly reduces the mechanical properties of the alloy electrode,while the dense oxide layer on the surface of the alloy increases the resistance to aluminum ion transport and thus affects the rate performance of the electrode,which limits the practical application of eutectic alloy electrodes.By uniformly grafting two-dimensional（2D）MXene layers on the surface of eutectic Al₉₇Ce₃(E-Al₉₇Ce₃)alloy with high aluminum content,eutectic alloy-based electrodes consisting of alternating internal monometallicα-Al phases and Al₁₁Ce₃ intermetallic phases and 2D artificial solid electrolyte interface（ASEI）layers on the surface can be obtained,and this highly flexible MXene grafted E-Al₉₇Ce₃ alloy electrode(MXene/E-Al₉₇Ce₃)can achieve a fast Al stripping/plating process.Among them,MXene can form the ASEI layer to isolate the electrolyte while weakening the passivation of the aluminum oxide layer to facilitate Al³⁺transport,and the eutecticα-Al phase and Al₁₁Ce₃ intermetallic compound phase act as the electroactive phase and 2D nanopattern,respectively,to enhance the transport driving force while inducing the reversible Al stripping/plating process.The synergistic effect of the eutectic alloy and ASEI layer ensures that the symmetric cell assembled with MXene/E-Al₉₇Ce₃composite electrode can achieve over 1000 hours of Al stripping/plating cycles with an overpotential of±54 m V and a Coulombic efficiency（CE）of over 97%.Soft-pack aqueous aluminum ion batteries assembled with MXene/E-Al₉₇Ce₃ anodes and Al_xMn O₂ cathodes supported with carbon cloth can exhibit excellent rate performance and cycling stability.When charged/discharged at a current density of 1 A g^-1,this battery was able to maintain 85%of its initial discharge capacity after 500 cycles(initial capacity～360 m Ah g^-1,based on the mass of Al_xMn O₂ loading).The excellent flexibility of the electrodes allows this soft-pack full battery to power micro-fans well under mechanical constraints.3.Manganese dioxide electrode with p-benzoquinone intercalation as a stable high-rate cathode material for aqueous aluminum ion batteriesAl³⁺storage process accompanied by strong electrostatic effects,difficult charge balance process and strong solventization problems make the layered transition metal oxide materials extremely susceptible to structure damage when storing Al³⁺,while the ultra-high transport resistance in the electrode also limits the rate performance of the cathode materials.Although organic materials represented by quinones can achieve good rate performance when performing Al³⁺storage,the properties of organic molecules make it difficult to balance cycling performance and energy density.The hydrothermal method can drive the in situ redox process of p-phenol（PE）and potassium permanganate（K_xMn O₄）molecules,and the positively charged BQ-Al³⁺can be assembled in situ with the reduced manganese dioxide（Mn O₂）sheets to obtain large layer spacing manganese dioxide electrodes with p-benzoquinone（BQ）intercalation（BQ-Mn O₂）.Among them,the BQ molecules can shield the high charge density of Al³⁺by coordination while maintaining the large layer spacing of Mn O₂,and the layered Mn O₂ structure can provide high theoretical capacity while suppressing the dissolution of BQ between its layers.With the synergy between organic molecules and TMOs,AIBs assembled with BQ-Mn O₂ cathodes and Zn₅₀Al₅₀ alloy anodes can exhibit specific capacities of over 380 m Ah g^-1 and energy densities of over 660 Wh kg^-1（based on the mass of BQ-Mn O₂ cathode）at low current densities for over 700 hours of cycling.Upon accelerated charge/discharge rates,this cell exhibits only slight polarization and minor capacity degradation,demonstrating its superior rate performance.