In a recent paper published in the journal Nano Energy, researchers developed a new composite anode material for high-energy batteries using multiphase interaction between lithium and graphitic carbon paper.
Study: Gradient lithiation to load controllable, high utilization lithium in graphitic carbon host for high-energy batteries. Image Credit: Illus_man/Shutterstock.com
The carbon paper-based anode has a dense lithium carbide top layer and a thin pure lithium bottom layer that facilitates uniform and stable lithiation/delithiation during cycling and high rate capacity.
Lithium in the Anode of Lithium-Ion Battery
The development of high-energy-density lithium-ion batteries (LiBs) has hit a roadblock because of the limited theoretical capacity of graphite (C) anode i.e. 372 mAh g-1. Li is usually present in the cathode and electrolyte of LiBs and its ion (Li+) acts as the charge carrier. Li has a high theoretical capacity of 3860 mAh g-1 and a low electrochemical potential of -3.04 V vs. standard hydrogen electrodes, and it performs multiphase interaction with carbon materials.
However, its practical application in the anode is obstructed by factors such as the formation of uncontrolled Li dendrites and fragile solid electrolyte interphase (SEI), and large volume changes during lithiation/delithiation.
Consequently, many pieces of research are ongoing to introduce Li into the graphite matrix to form a stable multiphase solid solution that could provide Li+ absorption sites and increase the theoretical capacity cap of graphite, simultaneously. Additionally, as the Li-C phases such as lithium carbide (LiC6) will host Li+, it will obliterate the volume change by suppressing the dendrite growth of Li.
About the Study
In this study, researchers synthesized a stable Li-C solid solution coated graphitic electrode by directly pouring molten Li on the highly graphitic carbon paper (CP). First, a thin uniform dense LiC6 layer was homogeneously coated on the surface of CP.
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The lipophilic (Li affinity) LiC6 layer induced a strong capillary force along with its pores that gradually sipped in the molten Li metal towards the LiC6 -CP interface and formed a Li-C phase gradient along the path. Also, a pure metallic Li layer was formed in between CP and LiC6 layers.
The infiltrated molten Li did not fill the inner space of the host CP, which favorably provides a buffer zone to accommodate the large volume change during Li+ lithiation/delithiation.
From the scanning electron microscopy (SEM) images, it was evident that the Li-CP/LiC6 electrode maintained a large amount of lithiophilic sites, high porosity, fast charge transportation paths, and low resistance to the passage of Li+ and causes uniform deposition, thus effectively accommodating dendrite-free volume changes.
The electrochemical measurements showed that the total Li capacity of the Li-CP/LiC6 electrode is about 8.5 mAh cm-2 after charging to 2.0 V at a current density of 1.0 mA cm-2, which was higher than both metallic Li and lithiated LiC6.
The X-ray diffraction (XRD) data indicated the Li-CP/LiC6 electrode maintained an intact porous structure, and the bottom Li layer was removed before the lithiated LiC6, which promoted the utilization of Li metal. Further, the carbon host had a porous structure, which indicated that the withering of the bottom Li layer had no ion transport limitation.
Additionally, as the metallic Li was completely consumed, the LiC6 participated in the delithiation process to replenish the Li layer and sustain the cell cycling.
The symmetric cell performance of the Li-CP/LiC6 electrode in a conventional carbonate-based electrolyte demonstrated good cycling stability with a much smaller voltage hysteresis for over 600 hours/300 cycles. Moreover, the small amount of metallic Li loading in the Li-CP/LiC6 electrode is gradually consumed, and delithiation of LiC6 was required to compensate for that, thus resulting in a slight increase in interfacial impedance.
The researchers developed a multiphase Li-CP/LiC6 anode for LiBs by directly depositing molten metallic Li on graphitic CP. The prepared electrode demonstrated excellent electrochemical stability, volume change suppression, and rated capacity. The suppression of dendritic growth of Li resolved the associated security concerns and the presence of Li in the anodes opened up a new pathway towards high-energy-density LiBs.
Tao, L., Ma, B., Luo, F., Xu, Z., Zheng, Z., Huang, H., Bai, P., Lin, F., Gradient lithiation to load controllable, high utilization lithium in graphitic carbon host for high-energy batteries, Nano Energy, 2021, 106808, ISSN 2211-2855, https://www.sciencedirect.com/science/article/pii/S2211285521010570