| Lithium secondary batteries have been widely used in mobile phones,laptops and other small digital electronic products,electric vehicles,aerospace,military and other important areas which have an even broader prospect for development because of their advantages of high energy density,long cycle life and low environmental pollution.With the higher energy density of lithium secondary batteries developed,the main way to increase energy density is to use high voltage cathode material on the one hand and lithium metal with extremely high theoretical capacity as negative electrode on the other hand.However,finding electrolyte materials matched above is a key factor which hinders the development of lithium secondary batteries.A semi-solid hybrid electrolyte is designed and proposed,and the performance of the hybrid electrolyte in high voltage lithium ion battery and lithium metal secondary battery is studied in this thesis.The main conclusions are as follows:One of the crucial challenge for developing high safety and high voltage lithium ion batteries is to find a reliable electrolyte system.The hybrid semi-solid electrolytes are obtained by incorporating silane-Al2O3?Al2O3-ST?into base electrolyte,which combines the merits of both solid electrolyte and liquid electrolyte.The semi-solid hybrid electrolyte has a higher ion mobility of 0.770.84,while the commercial electrolyte has only 0.30.The self-extinguishing time of decreased from 84.12 s g-1 with base electrolyte to 17.36 s g-1 with the hybrid electrolyte,and the flame retardancy was increased by nearly 4 times.Semi-solid hybrid electrolytes have no unfavorable reaction at 2.76.5 V and are resistant to high voltage.The conductivity of the hybrid electrolyte at room temperature is?8.799.98?×10-3 S cm-1 s cm-1 is very close to 10.39×10-3 S cm-11 of base electrolyte.The capacity retention is 99.1%after 200 cycles at 1C for LiNi0.5Mn1.5O4/Li cells with the hybrid electrolyte.Although the rate capacities show no obvious differences at low current rate?lower than 1C?,the cells with hybrid electrolytes?SSE-5 and SSE-10?owns higher discharge capacity at 2C and 5C.For example,the discharge capacity of SSE-10 is 132.4mAh g-1 at 2C and 129.1 mAh g-1 at 5C.While the capacity of the LiNi0.6Mn0.2Co0.2O2/graphite battery remains similar,nail-penetration tests indicate that LiNi0.6Mn0.2Co0.2O2/graphite battery with hybrid electrolyte showed no fire and smoke obviously enhanced safety than that using traditional liquid electrolyte.The maximum temperature detected is about 38.5°C.Meanwhile,the voltage only drops from 4.2 V to 3.8 V after 1 h for cell using hybrid electrolyte during nail-penetration tests.This work provides new insight on electrolyte design for high-safety high-voltage lithium ion batteries.Lithium metal are regared as the most power anode material in lithium metal batteries due to its negative electrochemical potential and high theoretical capacity,but uncontrolled lithium deposition is the potential safe problem to resolve.In this work,we continue the concept of hybrid electrolyte.By further optimizing the design of electrolyte component,a unique slurry-like hybrid electrolyte composed of liquid electrolyte and nanometric ceramic fillers silane-Al2O3nanosize ceramic particles is prepared,which combines the merits of both solid electrolyte and liquid electrolyte.Meanwhile,the slurry-like hybrid electrolyte have high ionic conductivity(3.89×10-3 S cm-1)and high lithium-ion transference number?0.88?.The self-extinguishing time of liquid electrolyte is 179.37 s g-1,but only 95.12 s g-1 for hybrid electrolytes.The flame retardancy was increased by 1.89 times.It is found that the hybrid electrolyte can form an interfacial layer which can conducts lithium ions on the surface of lithium metal.On the one hand,the interface layer can prevent the unfavorable reaction from the Li metal and the electrolyte.On the other hand,it can effectively inhibit the growth of lithium dendrite.Under the current density of 1mA cm-2,the cycle life of Li/Li symmetry cells with slurry hybrid electrolyte can be stabilized for 200 h.The cycle life of Li/Li cells using this hybrid electrolyte system is 10 times longer than that of conventional liquid electrolyte.While the electrolyte is used for Li4Ti5O12/Li cells,show the cycling stability after the cycle of 750cycles at 0.5C,the capacity of the electrolyte remains 150.1 mAh g-1,while the cell with liquid electrolyte is only 98.6 mAh g-1. |
PDF Full Text Request