Room Temperature Rechargeable Aluminum Battery And Its Key Materials

Environmental problems caused by the usage of fossil fuels,as well as the increasingly scarce of fossil energy make people start looking for new energy sources.Low-cost electrochemical energy storage system with high energy density is the key factor to utilization and development of new energy.Rechargeable aluminum battery is considered as a promising battery system used in energy storage devices,due to its great abundance,trivalent oxidation state,high volumetric energy density and inherent safety.Attempts to use aluminum as an electrochemical energy source have been made since the 1800s.However,fabrication of this battery working at room temperature didn't succeed until haloaluminate contained ionic liquids were used as electrolytes.To date no great success has been achieved due to difficulties with finding a suitable electrolyte and cathode material.This dissertation explains some of the author's efforts to overcome these difficulties.?1?Investigations of V₂O₅ nanoparticle cathode:This cathode is synthesized by directly depositing V₂O₅ on a Ni foam current collector.Rechargeable aluminum coin cells fabricated using the as-synthesized binder-free cathode delivered an initial discharge capacity of 239 mAh/g,which is much higher than that of batteries fabricated using a cathode composed of V₂O₅ nanowires and binder.An obvious discharge voltage plateau appeared at 0.6 V in the discharge curves of this binder-free cathode,which is slightly higher than that of the V₂O₅ nanowire cathodes with common binders?PVDF ans PTFE?.This improvement is attributed to reduced electrochemical polarization.?2?Investigations of a self-assembly V₂O₅·nH₂O nanoflake cathode:The V₂O₅·nH₂O nanoflakes directly grow on a 3D conductive stainless steel mesh substrate,prepared via a simple and green hydrothermal method.Well layered V₂O₅·nH₂O?n=0.3?nanoflake after heat-treatment at 300?show excellent electrochemical performance in secondary batteries with either monovalent or multivalent cation intercalation.The cathode with ultrathin V₂O₅·nH₂O nanoflake delivers an initial discharge capacity of 30 mAh/g and a stable capacity of 80 mAh/g after 100 cycles in Al-ion battery at 0.1-2.5 V potential range.?3?Investigations of ionic liquid electrolyte:By changing the anions,we can select and design suitable ionic liquid electrolytes for rechargeable aluminum batteries.In this paper,we first investigate the commonly used AlCl₃ based ionic liquids for a fully understanding of anion-effect,then develop a new ionic liquid to solve the problem facing the AlCl₃ based ionic liquids.For AlCl₃ based ionic liquids,on the one hand,both of the oxidative decomposition voltage and conductivity are found decreasing with reducibility of halide ion?Cl?Br?I?.On the other hand,with the AlCl₃ content increasing,the chloroaluminate anions changed?Cl^-?AlCl₄^-?Al₂Cl₇^-?.Therefore,ionic liquids with all Cl contained anions show the best performance and concentration of Al₂Cl₇^-is considered as a key factor in these ionic liquids when used as electrolyte.It is found that only Al₂Cl₇^-contained ionic liquids used in rechargeable aluminum battery show electrochemical activity.What's more,corrosion is found in Al₂Cl₇^-contained ionic liquid,and the degree varies with its concentration.Actually,appropriate degree of corrosion may help removing the oxide film on Al metal foil,so as to improve the charge/discharge performance.But severe corrosion shows the opposite effect and do harm to the compatibility of ionic liquid electrolytes.To solve the problem of corrosion and further improve the electrochemical window,a high-voltage non-corrosive Al?CF₃SO₃?₃/[BMIM]CF₃SO₃ ionic liquid electrolyte is developed,obtained by mixing 1-butyl-3-methylimidazolium trifluoromethanesulfonate?[BMIM]CF₃SO₃?ionic liquid with the corresponding aluminum salt?Al?CF₃SO₃?₃?.A high oxidation voltage?3.25V?is found,with good ionic conductivity at room temperature.However,it is found that the dense oxide film on Al surface can't be destroyed by Al?CF₃SO₃?₃/[BMIM]CF₃SO₃ ionic liquid,which blocks the reduction and oxidation of Al,further impact the performance of aluminum battery using this ionic liquids as electrolyte.To solve this problem,a method which adopts acidic AlCl₃ based ionic liquid to destroy the oxide film on Al anode is used.This method makes Al?CF₃SO₃?₃/[BMIM]CF₃SO₃ ionic liquid successfully applied in rechargeable aluminum battery with the pretreated Al anode,and it can also do help to other electrolytes which can't destroy oxide film by themselves.?4?Investigations of poly?vinylpyrrolidone??PVP?as a functional binder in aluminum-sulfur battery:By using PVP binder,a good charge-discharge cycling stability was achieved by commercially micron sulfur cathode in Al/S battery.What's more,it is confirmed for the first time that Al₂S₃ can be used as the cathode of aluminum secondary battery.It has been found that PVP as a binder for S cathode has a remarkable effect in suppressing the dissolution of polysulfides.Compared with the sulfur cathode using PTFE as the binder,the sulfur cathode with PVP as binder has the specific capacity as high as 450mAh/g with almost no capacity decay.