Achieving Uniform Li Plating/Stripping at Ultrahigh Currents and Capacities by Optimizing 3D Nucleation Sites and Li2Se‐Enriched SEI

Abstract Lithium (Li) has garnered considerable attention as an alternative anodes of next‐generation high‐performance batteries owing to its prominent theoretical specific capacity. However, the commercialization of Li metal anodes (LMAs) is significantly compromised by non‐uniform Li deposition and inferior electrolyte–anode interfaces, particularly at high currents and capacities. Herein, a hierarchical three‐dimentional structure with CoSe2‐nanoparticle‐anchored nitrogen‐doped carbon nanoflake arrays is developed on a carbon fiber cloth (CoSe2–NC@CFC) to regulate the Li nucleation/plating process and stabilize the electrolyte–anode interface. Owing to the enhanced lithiophilicity endowed by CoSe2–NC, in situ‐formed Li2Se and Co nanoparticles during initial Li nucleation, and large void space, CoSe2–NC@CFC can induce homogeneous Li nucleation/plating, optimize the solid electrolyte interface, and mitigate volume change. Consequently, the CoSe2–NC@CFC can accommodate Li with a high areal capacity of up to 40 mAh cm–2. Moreover, the Li/CoSe2–NC@CFC anodes possess outstanding cycling stability and lifespan in symmetric cells, particularly under ultrahigh currents and capacities (1600 h at 10 mA cm−2/10 mAh cm−2 and 5 mA cm−2/20 mAh cm−2). The Li/CoSe2–NC@CFC//LiFePO4 full cell delivers impressive long‐term performance and favorable flexibility. The developed CoSe2–NC@CFC provides insights into the development of advanced Li hosts for flexible and stable LMAs.


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(DOL) and 1,2-dimethoxyethane (DME) (v/v=1:1) with 1% LiNO3). The separator was Celgard 2400. The current density was set to 1 mA cm -2 during electrodeposition. Different Li deposition capacities (10 mAh cm -2 or 40 mAh cm -2 ) can be achieved by setting the specific electroplating time. Finally, after disassembling the cell in the glove box and rinsed with DOL, the Li/CoSe2-NC@CFC anode was obtained. In pouch cell test, the Li/CoSe2-NC@CFC anode with 1.5×4 cm 2 was prepared via electroplating in ultrasealed electrolytic cell and performed on a Bio-Logic VSP workstation. The electroplating current density and time were set as 10 mA cm -2 and 1 h, respectively.

Material Characterization
The SEM and element analysis were explored via an FEI Helios G4 CX dual-beam field emission scanning electron microscope equipped with an energy dispersive X-ray spectrometer (EDX). To avoid air pollution of Li in SEM tests, the cycled cells were disassembled in the glovebox and rinsed with 1,3-dioxolane (DOL). After drying in the glovebox, the cycled electrodes were put into a sealed container filled with Ar and then transferred into the SEM chamber as quickly as possible. TEM, SAED, and element distributions were obtained by JEOL JEM-2100F field emission transmission electron microscope equipped with EDX. XRD characterizations were performed through a Rigaku SmartLab with Cu Kα radiation. Similarly, after rinsing by DOL and drying in the glovebox, the as-prepared Li/CoSe2-NC@CFC anode was encapsulated in 4 the CR2032 Case (Kejing) with one side Kapton Window (10 mm) for further XRD analysis. XPS analysis was carried out by a Thermo ESCALAB 250 spectrometer. BET analysis was investigated by ASAP 2460 analyzer from Micromeritic.

Electrochemical Measurements
The batteries were assembled basing CR2025 coin cells in an Ar-filled glove box and measured via Neware battery cycler (CT-4008T, Shenzhen, China) at room temperature. The electrolyte was either-based electrolyte and the separator was Celgard 2400. To investigate the morphology evolutions of Li deposition on CoSe2-NC@CFC or CFC, Li//CoSe2-NC@CFC or Li//CFC cells were constructed and tested at 1 mA cm -2 with 10 mAh cm -2 or 40 mAh cm -2 .
To evaluate Li stripping/plating behaviors, two identical Li/CoSe2-NC@CFC anodes were assembled into symmetric cells. The capacity of Li pre-deposited in the CoSe2-NC@CFC was 10 mAh cm -2 for the cycling capacity of 1 mAh cm -2 and 40 mAh cm -2 for the cycling capacity of 5, 10, and 20 mAh cm -2 . The electrochemical impedance spectroscopy (EIS) was conducted on a Bio-Logic VSP workstation with a frequency range from 100 kHz to 1 mHz. In full cell tests, the Li/CoSe2-NC@CFC anode (10 mAh cm -2 ) was paired with LiFePO4 (LFP) cathode (active mass loading:~6 mg cm -2 ) to assemble the Li/CoSe2-NC@CFC//LFP cell. The LFP cathode was prepared by a blade-casting method basing a mixed slurry, which is consisted of LFP, carbon 5 black, and polyvinylidene fluoride (8:1:1 wt%) in N-methyl-2-pyrrolidone (NMP). In pouch cell test, the active area of the LFP cathode was 1.5×3.5 cm 2 (active mass loading:~10.97 mg).

Theoretical calculations
Theoretical calculations are performed using the Vienna Ab Initio Simulation Package Ead=Eadsorption-Esubstrate-ELi in which Eadsorption, Esubstrate, and ELi is the total energy of adsorbing Li on exposed surface, the total energy of substrate, and the total energy of Li, correspondingly.
Similarly, the configurations and adsorption energies of Li at the sites of pyrrolic N, pridinic N, graphitic N, oxidized N, and C sites on the graphite sheet can be obtained accordingly.
Finite elemental analysis 6 The finite elemental analysis was executed using COMSOL Multiphysics software, in which the chosen physics module was secondary current distribution. The size of the two-dimensional model was set as 20×15 μm 2 . The constructed nanostructures consist of vertical nanoflakes and embedded nanoparticles (corresponding to semicircles).
The height and width of nanoflakes were set as 2 and 0.2 μm, respectively, while the diameter of nanoparticles was 100 nm. The gaps of adjacent nanoflakes and top-bottom nanoparticles were set as 1.5 and 0.2 μm, respectively. The whole simulated area was full of the bulk electrolyte (1 M LiTFSI in DOL/DME (v/v=1:1)) with a conductivity of 1.1 S m -1 . [2] The performed current density was 10 mA cm -2 and the dynamic expression type was Butler Volmer. The simulated process was carried out in steady-state at room temperature. [3] 7 Figure S1. Low (a) and high (b) magnification SEM images of the CFC.        The cross-section SEM images in Figure S13 compare the volume changes of CoSe2-NC@CFC and CFC before and after 10 mAh cm -2 Li plating. As shown in  As shown in Figure S16a-l, after different cycles, the morphologies of bare Li and Li/CFC all engender the growth of Li dendrites. As the cycle continues, partial Li 16 dendrites will transform into "dead Li" and hinder the transport of Li + during the striping/plating process, resulting in the increase of internal resistance and overpotential. By comparison, Li/CoSe2-NC@CFC anodes maintain flat and dense morphology no matter after 20 cycles or 50cycles, which is beneficial to protect SEI integrity and suppress the formation of "dead Li", possessing the superior cycling performance ( Figure S16m-r).         Figure S19.