Investigation Of Two Issues In Lithium Ion Batteries And Selfpowered Energy Storage Devices

The energy crisis and environmental pollution are becoming more and more serious.As a result,clean and renewable energy systems are facing greater demands.Lithium ion batteries,lithium air batteries and solar cells are typical devices for clean energy storage or conversion and have attracted great attention recently.However,there are still many problems to solve.In this paper,we investigated two problems in lithium ion batteries and tried to integrate perovskite solar cells with energy storage devices.Li₂CO₃ commonly present on the surface of cathode materials in lithium ion batteries and in lithium air batteries as by-product.As it is electrochemically stable and hard to decompose,the performance of lithium ion batteries and lithium air batteries is lowered.To solve this problem,we prepared spinel and hexagonal LiCoO₂ with sol-gel method and used them as catalysts to promote the electrochemical decomposition of Li₂CO₃.The results reveal that spinel LiCoO₂ works better than hexagonal LiCoO₂.Li₂CO₃ could be completely decomposed under 4.25 V with spinel LiCoO₂ as catalyst.According to the potential curves of the compound,FTIR and GC-MS results,we proposed the decomposition mechanism of Li₂CO₃.Since Li₂CO₃ can be decomposed under low potential,it is believed to be a promising additive to compensate the lithium loss in lithium ion batteries.We also explored the catalytic performance of commercial CoO and Co₃O₄.As these cobalt oxides share the same crystal structure,it is found that the cobalt with higher valence shows better catalytic property.We prepared Sn₃?PO₄?₂ by co-precipitation method and used it as anode material in lithium ion batteries.The lithium storage mechanism of Sn₃?PO₄?₂ and the influence of cutoff discharge potential on it's structural reversibility were explored with potential curves,XPS,FTIR,XRD et al..In the initial discharge process,Sn₃?PO₄?₂ is firstly conversed into metallic Sn and inactive Li₃PO₄.When the battery is further discharged,the active Sn alloys with lithium while Li₃PO₄ keeps stable.When Sn₃?PO₄?₂ is fully discharged to 0.00 V,small amount of Sn₃?PO₄?₂ present after recharged to 3.00 V while most of Sn exist as big metallic Sn particles.In contrary,when the potential range is set to be 1.55-3.00 V,Sn₃?PO₄?₂ is partially reversible.That means the structural reversibility of Sn₃?PO₄?₂ in 1.55-3.00 V is much better than in 0.00-3.00 V.WO_x films with different thicknesses were prepared by PVD method and then used as electron transport layers in perovskite solar cells.The solar cells with 26 nm WO_x film as electron transport layer deliver the highest average power conversion efficiency which is 13.64%.When the glass substrate is replaced by flexible PEN/ITO,the average power conversion efficiency decreases to 10.02%.The lower transmittance of PEN/ITO and higher interface resistance are believed to be the main reasons for the lower performance of the flexible devices.Considering the rate performance and working potential,we chose carbon-based supercapacitor as the energy storage part in the early stage.The rigid and flexible self-powered devices show an overall efficiency of 1.35and 0.62%,respectively.