The growing demand for higher energy density batteries is increasing due to needs of electric vehicle (EV) [1]. Until now, it cannot exceed the one-time charging distance of an internal combustion engine vehicle, due to energy limit of batteries. Li metal anode (LMA) is one of the attractive anode candidates because of the lowest electrochemical redox electrode potential (-3.04 V vs. SHE) and the extremely high theoretical gravimetric capacity (3,860 mAh g^-1) compared to graphite anode (372 mAh g^‑1) [2]. However, uneven Li deposition causes dendritic growth leading to low Coulombic efficiency (CE) and safety hazards which is impeding the practical use of LMAs [3]. Recently, to suppress such dendritic growth, various solutions such as introduction of solid-state electrolyte (SSE) [4], artificial solid electrolyte interphase (ASEI) [5], 3D current collector (CC) [6], and lithiophilic materials [7] have been proposed.

Among the several approaches, introducing lithiophilic material on a CC is one of the facile and effective strategies to increase the lithiophilicity, and hence to induce the planar growth of Li. Also, assuming that electroplating is largely divided into two steps: nucleation and growth, lithiophilic material can change the intrinsic nucleation behavior by preferentially forming a different phases such as Li alloys [8]. Since the Li nucleation process significantly influences the final growth of Li, different cycling behaviors of LMAs would be expected depending on lithiophilic material [9]. As for the methods to adopt the lithiophilic materials, the electrodeposition is very attractive, since it can easily control the surface morphology, which might affect the Li deposition morphology and the related behavior. In this regard, we chose the tin (Sn) as a lithiophilic material, which can be deposited on Cu CC by electroplating, and moreover have a fast Li ion diffusion coefficient [10].

Specifically, in this work, we study the effect of surface morphology of lithiophilic Sn deposited on copper CC by testing Li deposition/stripping behavior for a LMAs. For different morphology, a direct current electrodeposition (DC) and pulsed electrodeposition (PED) were used.

Fig.1 is FE-SEM images of Cu@Sn with DC growth and PED growth. Fig.1 (a) shows Sn particles are growing without filling the pores. However, Fig.1 (c) shows Sn particles are growing with filling the pores. At Fig.1 (b) and (d), the morphology difference is conspicuous between DC and PED growth. Fig.1 (b) presents island growth in which nuclei grow on existing nuclei because there is only T_on without relaxation time. While, Fig.1 (d) shows that after rearrangement of deposited atom at T_off, new nucleation sites are created by continuously applying pulses, thereby obtaining the coalescence growth. At Fig.2, Cu@Sn (PED) shows the longer cycle life than bare Cu and Cu@Sn (DC) because Cu@Sn (PED) has an uniformly distributed nano Sn morphology, which provides more sites for Li nucleation to prevent dendritic growth.

References

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