Interface stabilization of LIB anodes-plastic crystal electrolyte via control of charge carriers and surface chemistry
Abstract
Forthcoming smart energy era, which will involve widespread use of flexible electronic devices, Internet of Things (IOTs), electric vehicles (EVs) and grid-scale energy storage systems (ESSs), is in urgent need of advanced rechargeable power sources with reliable/sustainable electrochemical performance and safety robustness. Considerable demand for the rechargeable batteries is also found in the Army applications, which include functional sensors, portable electronics (such as night vision devices, GPS, etc.), special force field equipment and long shelf life in missile systems. Undoubtedly, rational design and synthesis of new battery materials, along with characterization of their electrochemical properties, should be undertaken in order to address the aforementioned issues. Electrolytes play a viable role as an electrochemical reaction media in the batteries. Currently widespread electrolytes in the commercial lithium-ion batteries (LIBs) consist of lithium salts and carbonate-based solvents. They show well-balanced electrochemical attributes suitable for the state-of-the-art LIBs. However, their flammable characteristics and limited electrochemical stability at electrode interfaces have caused serious concerns on safety failures and long-term durability of the LIBs. Among numerous electrolyte alternatives reported to date, plastic crystal electrolytes (PCEs) have garnered considerable attention due to their unique physicochemical properties. The PCEs, which are composed of lithium salts and plastic crystals bearing good solvation capability, are characterized with unusual thermal stability and ionic transport behaviors. Succinonitrile (SN, NC-CH2-CH2-CN) is a representative organic matrix showing non-ionic plastic crystal behavior with a plastic crystalline phase in temperature range between around - 40 (a transition temperature from crystalline to plastic crystalline phase) to 60oC (from plastic crystalline phase to melted state). Due to the presence of trans-gauche isomerism involving rotation of molecules about central C-C bonds of SN, SN/lithium salt-based PCEs (SN-PCEs) provide high ionic conductivity of more than 10-3 S cm-1 at room temperature. Another salient benefit of the SN-PCEs is the superior thermal stability (negligibly volatile up to 150oC) and nonflammability. Despite these remarkable advantages, the SN-PCEs have not yet been used to LIBs mainly due to their poor reduction stability. The nitrile groups (-C?N) of SN are easily reduced at low potential around Li/Li+, resulting in the unwanted degradation of cell performance. This problem becomes more pronounced at lithium metal (that is a strong reducing agent) anodes. Here, we investigate interfacial phenomena occurring between the SN-PCEs and LIB anodes (including graphite or Li metal), with a particular focus on structural/electrochemical analysis of the charge carriers and anode surfaces. Based on fundamental understanding of these interface phenomena, we present an innovative strategy that can stabilize interface between SN-PCEs and LIB anodes, which eventually enables the use of SN-PCEs in LIBs as a promising alternative electrolyte beyond conventional carbonate-based ones. Our approaches to reach this goal are briefly described as follows: I. Molecular-level understanding of interfacial phenomena between SN-PCEs and LIB anodes. II-1. (from the SN-PCE viewpoint) Interface stabilization through control of configuration isomerism and ionic association in SN-PCEs. II-2. (from the LIB anode viewpoint) In-situ/ex-situ formation of artificial protective layers on LIB anode material surfaces via functional additives and surface modification.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 11, 2019
- Source ID
- W911NF1810016
Entities
People
- Sang-Young Lee
Organizations
- Army Contracting Command
- Ulsan National Institute of Science and Technology
- United States Army