Li-ion batteries are among the most promising, efficient and common high-energy-density systems for electrochemical energy storage. There have been increasing demands for high-performance, inexpensive and safe batteries for electronics, electric vehicles and other energy storage applications
In batteries, electrolytes play the role as the medium for the transfer of charges between a pair of electrodes i.e. cathode and anode. At present, gel polymer electrolytes (GPEs) have gained much attention compared to both solid polymer electrolytes and liquid electrolytes. Gel polymer electrolytes are faster charging/discharging, and potentially higher power density compared to liquid electrolytes. However, ion permeability of gel polymer electrolytes is orders of magnitude lower than that of liquid electrolytes, mainly because of the polymeric structure which limits the ion mobility. The development of high capacity anode to replace carbon-based materials, commonly used for commercial LIBs, is another active research area for high-performance LIBs. Li-alloying anodes (Si, Sn, Ge etc.) have much higher Li storage capacity than commercial carbon-based anodes.
Among them, Silicon (Si) has been identified as one of the best candidates. Si has a high theoretical specific capacity of 4200 mAh g-1, a very low lithiation potential < 0.5 V vs. Li/Li+, and is naturally abundant and environmentally benign. In this research by Pandey et al, two fabrication methods have been employed to form a stable interface between the gel polymer electrolyte and the Si-VACNF anode. The infiltrated gel electrolyte was able to effectively accommodate the stress/strain due to the very large Si volume change (up to 400%) during charge-discharge which has been a critical limiting factor for Si anodes. The Si-VACNFs electrodes show high specific capacity, good rate performance and long cycling stability in such a solid-like, flexible GPE. The results of this study may lead to the development of solid-state lithium-ion batteries using the vertical 3D nanostructured electrodes and may be applicable for novel flexible thin-film microbatteries.
Figure Legend:The figure shows the optical images of a flexible gel polymer electrolyte film, SEM images of a VACNF array sputter-coated with silicon shell as a Li-ion battery anode and the electrode infiltrated with the gel electrolyte film, the charge/discharge curves at specified cycles, and the long-term cycling stability.
Gaind P. Pandey1, Steven A. Klankowski1, Yonghui Li2, Xiuzhi Susan Sun2, Judy Wu3, Ronald A. Rojeski4, Jun Li*1Show Affiliations
- Department of Chemistry,Kansas State University, Manhattan, Kansas 66506, United States
- Department of Grain Science and Industry,Kansas State University, Manhattan, Kansas 66502, United States
- Department of Physics and Astronomy,University of Kansas, Lawrence, Kansas 66045, United States
- Catalyst Power Technologies, 200 Carlyn Avenue, Suite C, Campbell, California 95008,United States
This study demonstrates the full infiltration of gel polymer electrolyte into silicon-coated vertically aligned carbon nanofibers (Si-VACNFs), a high-capacity 3D nanostructured anode, and the electrochemical characterization of its properties as an effective electrolyte/separator for future all-solid-state lithium-ion batteries. Two fabrication methods have been employed to form a stable interface between the gel polymer electrolyte and the Si-VACNF anode. In the first method, the drop-casted gel polymer electrolyte is able to fully infiltrate into the open space between the vertically aligned core–shell nanofibers and encapsulate/stabilize each individual nanofiber in the polymer matrix. The 3D nanostructured Si-VACNF anode shows a very high capacity of 3450 mAh g–1 at C/10.5 (or 0.36 A g–1) rate and 1732 mAh g–1 at 1C (or 3.8 A g–1) rate. In the second method, a preformed gel electrolyte film is sandwiched between an Si-VACNF electrode and a Li foil to form a half-cell. Most of the vertical core–shell nanofibers of the Si-VACNF anode are able to penetrate into the gel polymer film while retaining their structural integrity. The slightly lower capacity of 2800 mAh g–1 at C/11 rate and ∼1070 mAh g–1 at C/1.5 (or 2.6 A g–1) rate have been obtained, with almost no capacity fade for up to 100 cycles. Electrochemical impedance spectroscopy does not show noticeable changes after 110 cycles, further revealing the stable interface between the gel polymer electrolyte and the Si-VACNFs anode. These results show that the infiltrated flexible gel polymer electrolyte can effectively accommodate the stress/strain of the Si shell due to the large volume expansion/contraction during the charge–discharge processes, which is particularly useful for developing future flexible solid-state lithium-ion batteries incorporating Si-anodes.
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