| At present,the use of rechargeable batteries is becoming more wide,and the requirements of rechargeable batteries is becoming more harsh,therefore lithium ion batteries have become very popular in the energy storage and conversion equipment.However,the following problems are gradually highlighte d.Among these problems,capacity degradation has become a major restraining factor,and it hinders the further development of lithium ion batteries.It is reported that trace water and corrosion of transition metal ions are severe for electrochemical properties.The existence of trace water is inevitable in the production process of lithium ion battery,which will lead to irreversible capacity loss of the battery,affect the formation of solid electrolyte interfacial film and result in the corrosion of the collector and cathode materials.The transition metal ions dissolving from cathode causes the loss of active material.At the same time,the transition metal ions migrate and deposit on the graphite anode resulting in serious damage to the solid electrolyte interfacial film.Meanwhile,partial metal ions insert into the graphite layer resulting in the fade of the anode capacity.Therefore,the present study focuses on investigating the failure mechanism about the cell performance caused by trace water and the transition metal ions.And the suppression measures have been proposed to solve the problem.There are three aspects of research in this parper.First,the effects of different amount of trace water in lithium hexafluorophosphate-ethylene carbonate / diethyl carbonate electrolyte and lithium bis(oxalate)borate-tetramethylene sulfone / diethyl carbonate electrolyte on the performance of lithium ion batteries have been systematically studied.The critical values of trace water in lithium hexafluorophosphate-ethylene carbonate / diethyl carbonate electrolyte and lithium bis(oxalate)borate-tetramethylene sulfone / diethyl carbonate electrolyte are 0.2113‰ and 0.5391‰,respectively(based on the battery failure standard that capacity retention after 100 cycles is under 85%.).Besides,the commercial electrolyte lithium hexafluorophosphate-ethylene carbonate / diethyl carbonate is used as reference electrolyte to study the inhibition effect of lithium bis(oxalate)borate as the electrolyte lithium salt on the manganese deposition of MCMB anode.It is noteworthy that lithium bis(oxalate)borate-tetramethylene sulfone / diethyl carbonate electrolyte system has excellent film-forming properties.Dense protective film can be formed on the surface of the graphite electrode,which can effectively inhibit the deposition of manganese.However,when the concentration of manganese in the electrolyte is too high,electrochemical adsorption will occur,and there is still a small amount of manganese ions can be detected on the surface of solid electrolyte interfacial film.These manganese ions will catalyze the decomposition of the electrolyte.In addition,the decomposition products deposited on the surface of the solid electrolyte interfacial film will further increase the cell impedance and reduce the cycle stability of the battery.Through the study of the first two parts,it is defined the mechanism of the destruction on the cell performance by trace water and metal ions A new elec trolyte system is built to restrain the damage of the trace water and the transition metal ions in the electrolyte on the batteries.Furthermore,the surface of graphite electrode is pretreated with lithium sulphate solution by spray deposition technique.Li/MCMB is pretreated by lithium sulphate,which shows excellent cycle performance,high capacity retention rate and low interface impedance.This modification plays an important role in improving the performance of lithium ion battery.Moreover,from the perspective of anode material and solid electrolyte interfacial film,this method can provide a new idea for suppressing the destructive effect on battery performance by trace water and transition metal ions in the electrolyte... |
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