Research On Synthesis And Performance Of Delithiated Li_1-xCoO₂ As Cathode Material

With environmental pollution and energy crisis becoming increasingly prominent,it has become an urgent task to develop new green resources.As a new category of high-energy and pollution-free energy,lithium battery,which can be divided into primary lithium battery and secondary lithium-ion battery,has attracted much attention.Since that the cathode material in secondary lithium-ion battery is not in a charged state initially,it is inapplicable for primary lithium to release electricity directly.In order to bring this cathode material into the aspect of primary lithium,this paper synthesized Li_1-xCoO₂ powder by using the method of electrochemical delithiation according to the charge-discharge principle of secondary lithium-ion battery.The Li_1-xCoO₂ cathode material of varying delithiated degree was obtained through controlling the specific charge-capacity.And then its elemental composition,phase structure,micro morphology,and thermal stability were characterized by ICP-AES,XRD,SEM,and TGA.It can be found that delithiated Li_1-xCoO₂ powder exhibited a homogeneous distribution and a high dispersivity,and still maintain the layered hexagonal crystal system.The chemical formula of Li_1-xCoO₂ charged to the specific capacity of 100.0,120.0,140.0,and 150.0 mA.h.g^-1 is in the following order: Li0.64 CoO₂,Li0.56 CoO₂,Li0.49 CoO₂,Li_0.45 CoO₂.Li_1-xCoO₂ will be decomposed at the temperature of 200⁴00°C,and the quality of O2 evolved from this reaction is linear related to the delithiated degree.It shows that while the delithiated degree is increased,at 1C rate,the specific discharged-capacity of Li-Li_1-x CoO₂ battery is increased,but its coulombic efficiency is reduced.Among them is Li-Li_0.45 CoO₂ battery,which displays the specific capacity of 115.0mA.h/g and the coulombic efficiency of 76.7%.Recharge cycles tests indicate that the capacity that it lost is made up of reversible part and irreversible part,and the latter is positively associated with the delithiated degree.Factors analysis of discharge performance in Li-Li_0.45 CoO₂ battery reveals that if the current is too large during charging process,the delithiation process will be tended to develop inhomogeneously,which can lead to more capacity losses;conductive additive plays a role of conducting electrons and absorbing electrolyte,so the discharge performance obtains a promotion when its content raises in some degree;in the coating process,the amount of binder have to be appropriate,otherwise the active materials will drop off or the battery impedance will increase,both of which will have a negative effect on discharge performance;not only the crystallization property of PVDF but also the structural stability of Li_1-xCoO₂ is related to the high-temperature baking process of pole piece,and on the whole treating for 4h at 120°C is the best optimal choice in this paper.It can be concluded from the research of storage performance that the electrochemical activity of Li_0.45 CoO₂ powder is not stable in air,however,it seemingly do not degrade the specific discharge-capacity in argon or in vacuum.Voltage delay and capacity loss have occurred in Li-Li_0.45 CoO₂ battery during storage process because of chemical self-discharge,therefore,maybe the battery owns some potential value only if designed into the construction of reserve model.