实用化条件下金属锂负极失效的研究

Failure mechanism of lithium metal anode under practical conditions

金属锂因其高理论比容量和低电极电势,被视为下一代高比能二次电池理想的负极材料之一.然而,其表面不稳定的固液界面膜及不均匀锂沉积等问题严重限制着其实际应用.目前,金属锂负极的研究大多采用温和的实验条件,这对于理解负极表界面的物理化学性质和揭示锂沉积规律等基础研究具有重要意义.但是,超薄锂负极(<50μm),低负极/正极面容量比(<3.0),低电解液量(<3.0 g·A·h^–1)等实用化条件是实现高比能金属锂电池(> 350 W·h·kg^–1))的前提.本文对金属锂负极在温和及实用化条件下的循环稳定性和负极表面形貌等进行比较,分析造成差异的原因,揭示金属锂负极在实用化条件下面临的挑战,并提出潜在的实用化金属锂负极的研究策略,以望促进高比能金属锂电池的发展.

Lithium(Li)metal is regarded as one of the most promising anodes in the next-generation high-energydensity rechargeable batteries due to its ultrahigh theoretical specific capacity and low reduction potential.Nevertheless,the unstable solid electrolyte interphase on the surface of Li metal anode and the nonuniform Li deposition seriously hinder its practical applications.Currently,mild conditions are employed in the researches of Li metal anode,which is of great significance for fundamentally understanding the physicochemical features of the anode interface and the mechanisms of Li deposition.However,practical conditions including ultrathin Li metal anode(<50μm),low negative/positive electrode areal capacity ratio(<3.0),and lean electrolyte(<3.0 g·A·h^–1)are the premise to realize high energy density of Li metal batteries(>350 W·h·kg^–1).Here in this work,the gaps of Li metal anode under mild and practical conditions in terms of the cycling stability and surface morphology are compared and the reasons for the gaps are analyzed carefully.The total quantity of active Li metal decreases and the utilization depth of Li per cycle has been greatly improved under practical conditions.Therefore,the huge volume fluctuation and uneven Li deposition result in ceaseless destruction and regeneration of solid electrolyte interphase,and thus consuming the lean electrolyte and generating a large quantity of dead Li rapidly.Consequently,the polarization voltage of Li metal anode increases rapidly and the cycling stability of Li metal batteries deteriorates evidently under practical conditions.Moreover,the electrochemical reaction of Li metal anode is accelerated while fast charge/discharge process is employed,which further aggravates the stability of Li metal anode.This work reveals the challenges of Li metal anode under practical conditions and present the perspectives for the further researches in practical Li metal anode,which conduces to the solid development of high-energy-density Li metal batteries.