Performance Studies Of Silica Gel Electrolytes On Rechargeable Hybrid Aqueous Batteries

Lithium-ion battery system(LiBs)has been demonstrated to be one of the most promising stationary power sources with high-energy,high-power density,long lifetime and light weight.Therefore,Li Bs have attracted the attention of scientists and have been studied widely.However,despite their remarkable performance,LiBs employ highly toxic and flammable organic solvents in the preparation of electrolytes and this causes safety hazards if used improperly.In addition,manufacture procedures of LiBs are complicated and expensive,partly because the electrolytes are sensitive to moisture and air.These ch allenging issues hinder the application of LiBs in the large-scale energy storage systems.In 1994,Dahn's group reported a new type of rechargeable lithium-ion battery using aqueous based electrolytes as replacements of organic based electrolytes.The newly developed system is namely the aqueous rechargeable lithium-ion batteries(ARLBs).Recently,rechargeable hybrid aqueous batteries(ReHABs)have been introduced.ReHABs use LiMn2O4 in the cathode,zinc foil as the anode,and an aqueous electrolyte containing Zn2+ and Li+ ions.There are several technical issues which must be solved to ensure the delivery of this system to the market.First,the ReHABs are apt to occur zinc deposition of dendritic crystals in charging and discharging process for a long period along reversible redox reaction of zinc on one side of a negative electrode so as to cause piercing of a separator and efficiency loss caused by battery short circuit.Second,similar to other battery systems,the ReHABs suffer from self-discharge.On the other hand,in application such as uninterruptible power supply(UPS),batteries consume electrical power under constant charging after they have been already charged to full capacity.This is because there is a back current inside the battery,which is named the float current.In ReHABs,higher float charge current is related with larger volume of oxygen being generated from the decomposition of water at high working potential.Last but not least,the poor water retention ability of ReHABs leads to pH and concentration change in the electrolyte which results in rapidly declining of the battery capacity.The work mainly included the following items:(1)Basic studies and performance evaluation of silica nanoparticles doped electrolytes on rechargeable hybrid aqueous battery batteriesSilica nanoparticles doped aqueous electrolytes have been prepared and implemented for the first time in rechargeable hybrid aqueous battery systems(ReHABs).Silica nanoparticles were doped into the liquid electrolyte with the initial aim to create a silica containing gel electrolyte.However,the 5% and 10% SiO2 doped electrolytes were viscous and could be easily absorbed in the Absorbed Glass Mat(AGM)separator and the whole system(doped electrolyte + AGM)immobilized after a few minutes.The AGM loaded with silica doped electrolytes remained wet after storage for weeks under ambient condition thanks to the water retention ability of nanoscale silica particles.The doped silica nanoparticles restrained deposition of zinc dendritic crystals,and reduced float charge current and self-discharge.The ReHABs assembled from the silica nanoparticles doped electrolytes provided high specific discharge capacity,up to 140 mAh ×(g LiMn2O4)-1 at 0.2 C,and the cyclability of such systems was significantly enhanced compared to the ReHABs assembled from conventional electrolytes.X-Ray Diffraction revealed that the anode of the batteries using SiO2 doped electrolytes were protected since only the XRD peaks of Zn were detected after the batteries were running 700 cycles of charge and discharge.(2)Basic studies and performance evaluation of different silica gel electrolytes on rechargeable hybrid aqueous battery batteriesFive different gel electrolytes have been constructed from silica gelling agents and the conventional liquid electrolyte.The gels are applied in the rechargeable aqueous gel electrolyte batteries for the first time.Silica powders with higher porosity require less quantity and shorter gelling time.Gels are likely to be hosted in the porous space of the gelling agents.Batteries using gel electrolytes exhibit similar or slightly higher specific discharge capacity,higher rate capability,and up to 10% higher cyclability with Li Mn2O4 as cathode and zinc foil as.Furthermore,all gel batteries exhibit smaller open circuit voltage drops,indicating longer shelf-life.(3)Basic studies and performance evaluation of fumed silica and ?-cyclodextrin gel electrolytes on rechargeable hybrid aqueous battery batteriesA gel electrolyte has been constructed from a thixotropic and a non-thixotropic gelling agent and applied in the rechargeable aqueous gel electrolyte batteries for the first time.Thermogravimetric analysis proved that the retention of gel electrolytes in AGM separator up on heating is higher than that of the conventional electrolyte.Batteries using gel electrolytes exhibit ca.10% higher in specific discharge capacity,higher rate capability,and higher cyclability with LiMn2O4 as cathode in the gel electrolyte.Furthermore,the electrodes of gel batteries are protected,dendrite formation on the Zn anode is suppressed as confirmed by scanning electron microscopy and chronoamperometry studies.Co-usage of the thixotropic and non-thixotropic gelling agents delivers synergy,which can't be obtained by using a single thixotropic gelling agent.(4)Basic studies and performance evaluation of fumed silica and PVA gel electrolytes on rechargeable hybrid aqueous battery batteriesIn this work,gel electrolytes constructed from fumed silica and PVA have been prepared and implemented first time in ReHABs.The gel electrolyte could reduce the drop of open-circuit potential and the self-discharge rate.When using fumed silica and PVA gel electrolyte in ReHABs,higher specific discharge capacity,lower self-discharge rate,lower float charge current density,higher rate capability and better cyclability have been demonstrated.Moreover,the gel electrolyte enables ReHABs to obtain even and smooth zinc deposition,effectively avoids production of the dendritic crystals,and thus greatly reduces probability of battery short circuit.