Research On High Voltage Electrolyte For LiN_i?0.5?Mn_1.5O₄ Cathode

Recently,lithium ion batteries have been widely used in communication devices like mobile phones,laptops as well as digital products due to its high energy density,high discharge voltage as well as long cycling life.The electrolyte now used is mostly in liquid,when it is applied in high voltage,it will encounter continuous decomposition,the dissolution of transition metals and the fast decay of discharge capacity.This paper will focus on enhancing the stability of nickel manganese acid lithium half cells under high voltage.Through the selection of solvents and additives,we can make the electrolyte work normally over 4.35 V and even 5 V without any decomposition.Firstly,?-butyrolactone?GBL?and glutaronitrile?GLN?are used as electrolyte additives for LiNi_0.5Mn_1.5O₄ cathode of lithium ion battery,we add these additives separately to the base electrolyte,which consists of EC?EMC?DEC and LiPF6 A series of tests indicate that GBL preferentially oxidizes on LiNi_0.5Mn_1.5O₄ forming a stable protective film,which prevents the subsequent oxidation decomposition of the electrolyte from taking place.On the contrary,GLN degrades the performance of nickel manganese acid lithium half cells.Although GLN has a wider electrochemical window,it can simply enable the cyclic stability at low current rate.When current is increased,the incompatibility of GLN with low voltage Li anode is enlarged.Secondly,the effects of 1 vol.%and 2 vol.%fluoroethylene carbonate?FEC?on the electrochemical performance of LiNi_0.5Mn_1.5O₄?LNMO?have also been investigated,and the results show that the cycling performance and rate capability of LiNi_0.5Mn_1.5O₄ have been improved.In base electrolyte,the capacities become 91.3 mA h g^-1 with a retention of 82.3%after 150 cycles at 1 C rate.In contrast,after 150 cycles the 1%FEC system reaches 106.7 mA h g^-1 with a 91.1%capacity retention,and the 2%FEC system achieves 113.5 mA h g^-1 with a 96.2%retention.2%FEC system can even maintain 105.7 mA h g^-1 at 2 C rate.Series of measurements exhibit that the preferential decomposition of FEC is beneficial to form a conductive film,which contains less compositions with low ion conductivity.What's more,2%FEC is more useful in generating a uniform and dense film than 1%FEC.