Stable lithium metal anode enabled by high-dimensional lithium deposition through a functional organic substrate

Abstract

The growth of lithium dendrites severely restricts the development of lithium metal batteries. In order to achieve the goal of dendrites-free lithium in principle, it is crucial and urgent to control nucleation and growth of lithium. Here, a functional organic layer of perylene-3, 4, 9, 10-tetracarboxydiimide-lithium (PTCDI-Li) is built on the lithium anode surface by in-situ chemical reaction of PTCDI and Li metal. PTCDI-Li, with high surface energy (-10.19 eV) and low diffusion barrier (0.89 eV), efficiently promotes disk-shaped high-dimensional nucleation by regulation of lithium ion flux upon lithium plating, leading to a dendrites-free morphology. When operating under a relatively high current density of 10 mA cm⁻², the Li | Li symmetrical cells with PTCDI-Li exhibit outstanding cyclic stability for 300 hours with ultralow overpotential of 400 mV, superior to the most of the reported lithium anode. The corresponding PTCDI-Li batteries show high specific capacity and enhanced cycle life. We anticipate that this strategy of regulation of lithium deposition from one-dimensional to high-dimensional opens a new horizon in the development of dendrites-free Li anodes.

Introduction

Lithium (Li) metal is the key component for the next generation high-energy-density lithium-sulfur and lithium-oxygen batteries because of its ultra-high theoretical specific capacity (3860 mAh g⁻¹), lowest negative electrochemical potential (-3.040 V vs. the standard hydrogen electrode) as well as the low density (0.59 g cm⁻³) [1], [2], [3]. Despite the considerable advantages, the practical application of Li metal anode is severely hindered by the formation of Li dendrites that stem from non-uniform Li nucleation and deposition during repeated plating/stripping process [4], [5], [6], [7], [8], [9], [10], [11]. The dendrites will be broken when it develops to a certain extent, causing “dead lithium”, which can deteriorate electrochemical performance. More severely, the dendrites will penetrate the separator, resulting in a short circuit and a serious safety hazard [10], [12].

To address the above mentioned problems of dendrites, many efforts have been made including tailored liquid electrolytes and an artificial solid electrolyte interphase (SEI) [8], [11], [13], [14], [15], [16], [17], [18], [19]. Tailoring liquid electrolytes is considered to be an efficient method to stabilize the Li anode by in-situ formation of functional inorganic components such as Li₃N [20], Li₃PO₄ [21], Al₂O₃ [22], Li₂S [23], and LiF [24], which is beneficial for formation of stable SEI. However, the stable SEI layer is at the cost of electrolyte decomposition during long-time cycling, leading to battery failure. Besides, another effective way to inhibit Li dendrites is to construct artificial SEI via polymers with high modulus. Recently a variety of polymers, such as fluoropolymers (PVDF [25], PVDF-HFP [26]), polyacrylic acid (PAA) [27], polyimide [28], poly(dimethylsiloxane) (PDMS) [29], poly(ethylene oxide) (PEO) [30] and so on [15,31], have been developed to achieve uniform lithium anode through the surface engineering. Undoubtedly, these methods can gain considerable success in inhibiting lithium dendrites. However, the protective layer is readily broken and separated from Li electrode due to the large volume changes during cycling [32], [33]. Therefore, it is urgent and significant to suppress Li dendrites formation via regulating nucleation and growth of lithium metal.

In principle, the morphology of plated lithium is largely determined by the nucleation structure [34], [35], [36], [37] and the succedent growth of nuclei [38], [39], which is affected by the surface energy and diffusion barrier. High surface energy can generally promote high-dimensional nucleation due to the possible binding reaction [29], [39], [40], [41], [42]. Meanwhile, low surface diffusion barrier facilitates uniform homomorphism rather than local accumulation because low barrier is beneficial to releasing surface tension and combining surface atoms to form a complete layer [35], [43], [44], [45], [46], [47]. Therefore, it is feasible to construct artificial layer with higher surface energy and lower diffusion barrier to achieve dendrites-free lithium anode via high-dimensional nucleation.

In this work, we fabricate an organic functional layer (PTCDI-Li) by coating perylene-3, 4, 9, 10-tetracarboxydiimide (PTCDI) on the surface of lithium metal electrode via in-situ chemical reaction. The PTCDI-Li, with both higher surface energy of -10.19 eV to Li atom and lower diffusion barrier, can guide the uniform nucleation and growth of Li metal, achieving dendrites-free Li metal anode. Furthermore, the PTCDI-Li can remit volume changes due to the formation of denser and uniform lithium layer derived by high-dimensional lithium growth. Therefore, the PTCDI-Li demonstrate superior cyclic stability for 300 h even at ultrahigh current density of 10 mA cm⁻². More importantly, when the stable Li metal anodes are applied to lithium-sulfur batteries, the cells show excellent cycling life with high Coulombic efficiency.