Study On Multifunctional Separator And Electrolyte For Lithium Metal Batteries

Lithium(Li)metal batteries integrating transition metal oxide cathode with high specific capacity and Li metal anode constitutes a promising energy storage device due to its high energy density.The realization of high-specific-energy Li metal batteries should be based on practical conditions,such as ultrathin Lianode(<50?m),low negative/positive electrode areal capacity ratio(N/P<3.0),and lean electrolyte(<3.0g·Ah^-1).However,the limitd performance of Li metal batteries mainly due to the unstable solid electrolyte interphase(SEI)on Li anode and the uneven Li deposition.Based on the above problems,this work is mainly divided into the following aspects:Firstly,transition metal oxide materials have become important cathode materials for the next generation of high-specific-energy secondary batteries due to their high process maturity and good cycle stability.However,transition metal ions,such as Mn ions,can dissolve from cathode,migrate to anode,which prevents the application of almost Mn-based cathode.The effect of the dissolution of manganese(Mn)ions on the formation of SEI and the deposition of Liwas studied by introducing nonaqueous Mn(TFSI)₂ into the carbonate electrolyte through an electrolytic cell.It is found that Mn ions can diffuse to the anode,participate in the formation of SEI,induce uneven nucleation of Li.In addition,Mn ions can corrode the Li,deteriorate the overall performance of the battery.In response,a multifunctional separator is designed to prevent the migration of Mn ions due to its ion selective permeability,and protect the integrity of the anode and SEI.Thus,the cycle performance of the Li metal battery under practical conditions was extended from 62cycles to 100 cycles.This work provides a novel and practical strategy suitable for existing Li-ion and next-generation batteries.Secondly,in order to solve the problem of poor cycle life of ultrathin Lianode under practical conditions,glycolide(GL)was demonstrated as an electrolyte additive in pristine localized high concentration electrolyte(LHCE).This work found that GL decompose before LiFSI to participate in the formation of SEI,and enrich the components with C=O functional group in LiF-rich SEI,further promoting the uniformity of Lideposition and decreasing the accumulation of dead Li.The cells with GL additives delivered stable cycling performance of 175 cycles in comparison to 86 cycles without GL additives in Li|LiNi_0.5Co_0.2Mn_0.3O₂(NCM523)cells with an ultrathin Limetal anode(50?m)and a high loading NCM523 cathode(3 mAh·cm^-2).This work provides the design of electrolyte additives for stabilizing ultrathin Li anode.Finally,in view of the high-specific-energy of Limetal batteries,the challenges faced by Limetal anode under mild experimental conditions and practical test conditions were compared and analyzed.It was pointed out that the realization of high-specific-energy Li metal batteries needs to be based on practical conditions.It is characterized by ultrathin Li metal anode,trace electrolyte and a high single cycle utilization rate for anode.Then,the huge volume fluctuation and uneven Li deposition result in ceaseless destruction and regeneration of SEI,and thus consume the lean electrolyte and generate a large quantity of dead Li rapidly.Therefore,according to the characteristics of Li metal anode under practical conditions,the corresponding anode protection strategy is put forward,which has more significance for the practical development of Li metal battery.