Electrochemical Properties of the Interface Modified Li-Metal All Solid State Battery (Li/LLZO/LVO cell)

Abstract

As an anode material, Li metal is a most promising because of a low electrochemical potential(−3.045 V vs the standard hydrogen electrode), high theoretical capacity(3860 mAh/g), low density (0.534 g/cm3 ), and high electrical conductivity. However, a Li-metal anode battery is limited to use because of poor safety and electrochemical instability because of dendritic growth and “dead-lithium” outbreak during cycling in a flammable liquid electrolyte system. 1-3 The dendrite growth on the electrode surface is mainly caused by the localization of current due to the heterogeneous SEI film on the surface and the high current rate during cycling. 4 In order to overcome a dendrite growth behavior, there are many trials reported such as, Li metal morphology change(ref), coating the metal surface(ref), or adding a surfactant in the electrolyte. In addition, applying a solid state electrolyte (SSE) instead of a liquid electrolyte, it may overcome the disadvantage of a flammable electrolyte in the Li-metal battery.5There are two types of solid state electrolyte systems, such as a sulfidic electrolyte (i.e. LGPS(Li10GeP2S12)) and an oxide-based electrolyte(i.e. LLZO(Li7La3Zr2O12)). The former has very high ionic conductivity (12x10-3Scm-1). 6 Also, due to its ductile mechanical properties, it doesn’t require high pressure and temperature to manufacture the efficient solid state electrolyte pellet. 7, but it causes byproduct when exposed to reactive gases, humidity and lithium metal. 8Otherwise, an oxide-based electrolyte like LLZO has high ionic conductivity and is chemically and electrochemically stable with lithium metal anode. 9,10 However, high energy (1100oC, 300Mpa) is required to fabricate the efficient LLZO electrolyte. 11 and it also has the disadvantage of poor contact with the electrode due to its rigid mechanical properties.To be a true meaning of the Li-metal all solid state battery (ASSB), the Li-anode metal should be an energy (or ion) source. Therefore, non-lithiate materials such as sulfur or O2 should be coupled as a cathode material. Though they are still more works to use in the cell, Sulfur and O2 are attracting attention as a next-generation cathode material for lithium metal batteries due to their high theoratical capacity. 15,16 Instead, the LiV3O8 may be a proper non-lithiated cathode material to test a Li-metal ASSB, because its stability and electrochemical properties are already reported. 17, 18major obstacles at each constituents are numbered: (1) dendritic growth on the Li metal anode surface, (2) inappropriate contact at the anode/solid electrolyte interface, (3) poor ionic conductivity caused by less compacted solid electrolyte materials, (4) inappropriate contact at the solid electrolyte/ cathode interface, (5) poor ionic and electronic conductivity caused by less compacted cathode materials. Of course, more problems such as by-products due to every reactions, intervention of side reaction, and enhanced mechanical properties of the electrode materials also overcome to be a commercial Li-metal ASSB.The major purpose of the this research, however, builds a Li-metal ASSB system in which Li-metal used as an anode and understands the electrochemical performances of the Li/LLZO/LVO secondary batteries.