Research On The Surface Structure Regulation And Cycle Stability Of Lithium Metal Anode

Lithium metal is the key material most likely to make new energy batteries exceed 500 Wh Kg^-1energy density because of its highter theoretical specific capacity(3860 m Ah g^-1)and lowest reduction potential（-3.04 V vs.standard hydrogen electrode）,which is considered the"Holy Grail"anode for next-generation high energy density battery.However,the practical application of lithium metal anode suffers from poor cycle stability and low Coulombic Efficiency.The root causes of the above problems are as follows:On the one hand,there is a serious side reaction between the lithium metal anode and electrolyte,which generates an unstable solid electrolyte interface,leading to the uneven deposition of lithium metal and the growth of lithium dendrites.On the other hand,the lithium metal anode will undergo huge volume expansion during the cycles.To solve the above problems,we propose a strategy to construct a lithiophilic three-dimensional current collector.It can increase the specific surface area of lithium metal anode,reduce the nucleation potential and local current density of lithium metal anode,promote the uniform deposition/stripping of lithium metal.Finally,the cycle stability of the lithium metal anode is significantly improved.The main contents of this dissertation can be summarized as follows:1.Basing on the problem of poor cycling stability of lithium metal anode,we propose a silver-containing three-dimensional current collector for lithium metal battery.Compared with conventional lithium metal anode,on the one hand,the introduction of silver-containing three-dimensional current collector increases the specific surface area of lithium metal anode and reduces the local current density.On the other hand,the introduction of lithiophilic of silver provides a large number of sites for nucleation of Li⁺and reduces the nucleation potential.It promotes the uniform nucleation and growth of lithium metal and improves the cycle stability of lithium metal anode from 450 hours to 2100 hours.By regulating the amount of lithium metal deposition/stripping,we find that the introduction of silver-containing three-dimensional current collector is more effective in improving cycling stability than conventional lithium metal anode at high areal specific capacity.The underlying reason is that more lithium is deposited on the silver-containing three-dimensional current collector,which reduces the amount of lithium deposited on the lithium sheet.Further,we regulated the deposition current density and found that the introduction of silver-containing three-dimensional current collector still has better cycling stability.We applied it to Li|LFP battery,and the performance of battery with the introduction of silver-containing three-dimensional current collector was even better with a stable 400 cycles at a current density of 0.5 C with 11.5 mg cm^-2surface loading.In contrast,the performance of the conventional Lithium metal battery degrades sharply after 250 cycles.2.In order to solve the problem of incompatibility between anti-high-voltage ester electrolyte and lithium metal anode（severe side reactions）,we introduced 1,3-dimethyl-2-imidazolinone（DMI）with high Li NO₃ solubility into the ester electrolyte so that Li NO₃ could be applied in the ester electrolyte system.Li NO₃ is involved in the reduction reaction in the ester electrolyte to produce an artificial solid electrolyte interphase with rich Li₃N.Li₃N,as a fast ion conductor,can build fast ion channels on the lithium metal anode,improve the ionic conductivity of Li⁺,promote the uniform deposition/stripping of Li⁺,and improve the cycle stability and Coulombic Efficiency of the lithium metal anode.Compared with the conventional ester electrolyte,the electrolyte with the addition of DMI and Li NO₃ increased the Coulombic Efficiency of Li|Cu battery from 94.6%to 97.4%and the cycling stability from 100 to 160 cycles.At 1 m A cm^-2-1 m Ah cm^-2,the electrolyte with the addition of DMI and Li NO₃ improved the cycle life of Li|Li symmetric battery from 400 to 1400 h compared to the conventional ester electrolyte.In the Li|LFP battery,the electrolyte with the addition of DMI and Li NO₃ was able to run 450 cycles at a current density of 1 C with 96%capacity retention.In comparison,the conventional ester electrolyte was only able to run for a stable 350cycles.