To investigate the degradation mechanisms of electric double-layer capacitor ͑EDLC͒ components using 1.0 M triethylmethylammonium ͑TEMA͒ tetrafluoroborate ͑BF 4 ͒ in propylene carbonate ͑PC͒, the failure-mode processes of positive and negative electrodes were characterized as a function of the applied voltage ͑2.5-4.0 V͒. When the cell voltage ranges below 3.0 V, no impedance spectra or surface morphology changes were observed, indicating that no side reactions occur in this case. In the voltage range from 3.0 to 3.7 V, the exfoliation of graphene layers in activated carbon ͑AC͒ and the formation of cracks were observed in the positive electrode over 4.9 V vs Li/Li + possibly due to the gasification of surface functional groups with adsorbed water. On the negative electrode, the adsorbed water is electrochemically reduced to H 2 gas and OH − . The generated OH − induces the Hoffman elimination of TEMA + and activates the hydrolysis of PC. These water-induced side reactions could be the most critical factors for higher voltage operation. In the higher voltage range ͑over 3.7 V͒, the accumulation of solid electrolyte interface films by electrochemical oxidation and the reduction of PC were observed for both electrodes, indicating that the electrochemical oxidation and the reduction of PC on the AC surfaces occur above 5.2 V and below 1.5 V vs Li/Li + , respectively.Electric double-layer capacitors ͑EDLCs͒ are attracting much attention as one of the potential devices for energy regeneration of strong hybrid or plug-in hybrid electric vehicles because of their higher power densities ͑1-10 kW kg −1 ͒ compared to other energy devices, such as Li-ion batteries ͑0.1-1 kW kg −1 ͒. However the weakness of the EDLC is its low energy density ͑10 Wh kg −1 ͒, which cannot reach the target values ͑ca. 20 Wh kg −1 ͒ required of the hybrid vehicles by the Department of Energy and others. EDLCs can store electric charge in an electrical double layer at the electrode-electrolyte interface. Because the energy density is a product of capacitance and voltage, increasing the capacitance or voltage is necessary to enhance energy density. Increasing the voltage is more effective because the energy density increases in proportion to voltage squared.Activated carbons ͑ACs͒ have been widely used as electrode material because of their high specific surface area ͑1000-2000 m 2 g −1 ͒, immediate availability, and low cost. 1 Nonaqueous electrolytes consisting of acetonitrile ͑AN͒ or propylene carbonate ͑PC͒ solutions with 1 M tetraethylammonium ͑TEA͒ tetrafluoroborate ͑BF 4 ͒ 2-5 are used in commercial EDLCs because they permit a wide operating voltage ͑2.5-2.7 V͒.Recently, new approaches have been suggested by several researchers to achieve the target values of the hybrid vehicles. These approaches can be classified into three types according to the method as follows:1. Multifunctional nanoarchitectures. To optimize the ionic and electronic conductivities of electrode materials with charge-storage functionality, nanoscale structuring ͑nanostr...
Lithium titanium oxide (LiTiO)-based cells are a very promising battery technology for ultrafast-charge-discharge and long-cycle-life batteries. However, the surface reactivity of lithium titanium oxide in the presence of organic electrolytes continues to be a problem that may cause expansion of pouch cells. In this study, we report on the development of a simple and economical grafting method for forming hybrid polymer-LiTiO nanoparticles, which can be successfully applied in lithium-ion batteries. This method utilizes a low-cost and scalable hydrophobic polymer that is applicable in industrial processes. The hybrid materials demonstrated exceptional capability for preventing the degradation of cells in accelerated aging and operating over 150 cycles at 1C and 45 °C.
Lithium titanium oxide (Li4Ti5O12)-based cells are a promising technology for ultra-fast charge-discharge and long life-cycle batteries. However, the surface reactivity of Li4Ti5O12 and lack of electronic conductivity still remains problematic. One of the approaches toward mitigating these problems is the use of carbon-coated particles. In this study, we report the development of an economical, eco-friendly, and scalable method of making a homogenous 3D network coating of N-doped carbons. Our method makes it possible, for the first time, to fill the pores of secondary particles with carbons; we reveal that it is possible to cover each primary nanoparticle. This unique approach permits the creation of lithium-ion batteries with outstanding performances during ultra-fast charging (4C and 10C), and demonstrates an excellent ability to inhibit the degradation of cells over time at 1C and 45 °C. Furthermore, using this method, we can eliminate the addition of conductive carbons during electrode preparation, and significantly increase the energy density (by weight) of the anode.
Lithium titanium oxide (LiTiO)-based electrodes are very promising for long-life cycle batteries. However, the surface reactivity of LiTiO in organic electrolytes leading to gas evolution is still a problem that may cause expansion of pouch cells. In this study, we report the use of Schiff base (1,8-diazabicyclo[5.4.0]undec-7-ene) as an additive that prevents gas evolution during cell aging by a new mechanism involving the solid electrolyte interface on the anode surface. The in situ ring opening polymerization of cyclic carbonates occurs during the first cycles to decrease gas evolution by 9.7 vol % without increasing the internal resistance of the battery.
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