An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
A nanolayer of surface liquid phase in equilibrium with the bulk solid is responsible for the low grain boundary resistance in the solid electrolyte LiCl·DMF, as supported by a combination of experiment, theory, and modelling.
Electric vehicles’ (EVs’) more-limited driving range and longer charging times—compared with gasoline vehicle refueling—cause range anxiety that inhibits mass adoption of EVs. Extreme fast charging (XFC) is the ability to charge batteries in a length of time (i.e., ~10 minutes or less) comparable to that required to refuel gasoline vehicles [1]. The cell performance and aging mechanisms under XFC conditions are quite distinct from those seen under slow charging conditions. Among the various XFC challenges, Li-plating on the anode is the cause of poor cell performance, with severe capacity fade, dendrites growth and internal shorts that could lead to catastrophic safety issues [2]. Literature reports on electrochemical (EC) Li detection, mostly at sub-zero temperatures and moderate-to-high charging rates, show Li plating displaying higher-favorability, reliable plating-driven mixed potential dynamics [3-5]. Those EC signatures have not been evaluated extensively for fast-charging conditions. Our study focuses on the sensitivity and reliability of EC Li-plating signatures at varying XFC conditions with long-term cycling and aging. The global EC signatures investigated were coulombic efficiency (CE), incremental capacity (dQ/dV), differential voltage (dV/dt), and end of relaxed charge (EOC) voltage on moderate loading Li/graphite and graphite/NMC532 coin cells and graphite/NMC532 single-layer pouch cells under XFC conditions at 25°C [6]. The sensitivity and reliability of investigated signatures vary with cell-to-cell and cycling conditions. For example, the sensitivity and reliability of dQ/dV is good with moderate C-rate lithiation and reasonable de-lithiation (C/5) conditions. With increasing C-rate (e.g., 6C), dQ/dV sensitivity decreases even under the same discharge (C/5) conditions. The dV/dt signatures at various states-of-charge with 6C-lithiation conditions varies with cell-to-cell and cycling conditions. In all cases, the dV/dt signature appears during initial cycling at different relaxation times, intensities, but within few cycles, the signal strength decreases and/or disappears even though CE and EOC EC signatures confirm continuous Li plating on the graphite electrode. The EC Li-detection signatures in half-cells, full cells and full pouch cells align with each other within the experimental error. Long-term and continuous reliability of Li-plating detection with EC signatures is still an issue for XFC conditions. Ahmed, S., et al., Enabling fast charging – A battery technology gap assessment. Journal of Power Sources, 2017. 367 : p. 250-262. Santhanagopalan, S., P. Ramadass, and J. Zhang, Analysis of internal short-circuit in a lithium ion cell. Journal of Power Sources, 2009. 194 (1): p. 550-557. Campbell, I.D., et al., How Observable Is Lithium Plating? Differential Voltage Analysis to Identify and Quantify Lithium Plating Following Fast Charging of Cold Lithium-Ion Batteries. Journal of The Electrochemical Society, 2019. 166 (4): p. A725-A739. Petzl, M. and M.A. Danzer, Nondestructive detection, characterization, and quantification of lithium plating in commercial lithium-ion batteries. Journal of Power Sources, 2014. 254 : p. 80-87. Schindler, S., et al., Voltage relaxation and impedance spectroscopy as in-operando methods for the detection of lithium plating on graphitic anodes in commercial lithium-ion cells. Journal of Power Sources, 2016. 304 : p. 170-180. Tanim, T.R., et al., Electrochemical Quantification of Lithium Plating: Challenges and Considerations. Journal of The Electrochemical Society, 2019. 166 (12): p. A2689-A2696.
Polyoligomeric silsesquioxanes with eight (LiNSO2CF3) groups can be dissolved at very high loadings into tetraglyme, forming solvent-in-salt electrolytes, and stable colloids with increasing amount of tetraglyme. Li+ions can migrate by diffusive or coordinated hopping motions. HightLi+and conductivities are obtained.
Room temperature ionic liquids (RTILs), which are salts with low temperature melting points, have been investigated as electrolytes in electrochemical devices 1 , since they are nonvolatile (and as a result often non-flammable), and therefore safer than conventional aprotic liquid electrolytes, and have useful electrochemical stability windows (> 4V) 2 . However, they are typically more viscous (30-200 cP vs ~ 1 cP) than conventional aprotic or aqueous solvents, and therefore less conductive (0.1 to 18 mS/cm). Ion gels are ion conducting liquids such RTILs immobilized in a polymer matrix, forming a solid polymer electrolyte (SPE). They have become increasingly important as components in polymer electrolytes 3 for potential use as flexible solid-state electrochemical devices such as separators in lithium ion batteries and gate insulators in organic thin-film transistors (OTFTs). Immobilization of the RTIL can be achieved using gelators that participate in chemical crosslinking reactions (e.g. methylmethacrylate) 7 or form physical crosslinks. Physical gelation can be achieved with block copolymers, where one component (polyethylene oxide) solvates and the other component (polystyrene) is immiscible in the IL, or poly(vinylidene fluoride)-hexafluoropropylene copolymers (PVDF-HPF), where the crystalline component forms the crosslink sites. Here, methyl cellulose, a natural, renewable, environmentally friendly, abundant and inexpensive natural polymer, is used as the gel former, and combined with the ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (referred to here PYR 14 TFSI) to form tough, temperature stable ion gels. The detailed procedure for making the ion gels is presented in figure 2.The morphology of the ion gels, shown for the 90/10 composition ( Figure 2 ), is a volume spanning, random 3-D network of nanometer diameter MC fibrils. Linear fibers can form gels through their topological interactions alone, i.e., without cross-links, provided the fibers are sufficiently long. Although the network looks dense (Figure 2 ), it is the result of its collapse upon removal of the 90% liquid component. The phase separated morphology of the PYR 14 TFSI/MC ion gels results in both excellent mechanical properties as well as high ionic conductivities ( Figure 1 ). As expected, the storage moduli increase and ionic conductivities decrease with MC content. Room temperature moduli > 1 GPa are achieved for all compositions with < 60% PYR 14 TFSI and the PYR 14 TFSI/MC = 90/10 and 80/20 have respectable RT moduli of 0.15 GPa and 0.75GPa, respectively. The frequency dependence of both the storage and loss moduli for the PYR 14 TFSI/MC = 90/10 composition, show solid behavior over the whole frequency range. In summary, we have developed a facile route for the preparation solid polymer electrolyte ion gels from PYR 14 TFSI/MC. These ion gels have the highest combined moduli and ambient ionic conductivities (> 1 x 10 -3 S/cm) to date. These favorable properties are attributed to the immiscibility of PYR 14 TFSI in MC, which permits the ionic conductivity to be independent of the MC, and the high T m and T g of the MC fibrils. References 1. Galinski, M.; Lewandowski, A.; Stepniak, I., Ionic liquids as electrolytes. Electrochimica Acta 2006, 51, (26), 5567-5580. 2. Lewandowski, A.; Swiderska-Mocek, A., Ionic liquids as electrolytes for Li-ion batteries-An overview of electrochemical studies. Journal of Power Sources 2009, 194, (2), 601-609. 3. Susan, M. A.; Kaneko, T.; Noda, A.; Watanabe, M., Ion gels prepared by in situ radical polymerization of vinyl monomers in an ionic liquid and their characterization as polymer electrolytes. Journal of the American Chemical Society 2005, 127, (13), 4976-4983. Figure 1
A solid polymer electrolyte with high ambient temperature conductivity, 4 × 10−4 S cm−1, and transference number, tLi+ = 0.6, is formed from blends of polyethylene oxide (PEO) and a multi-ionic polyoctahedral silsesquioxane lithium salt, POSS-phenyl7(BF3Li)3, with Janus-like properties. A two-phase morphology is proposed in which the hydrophobic phenyl groups cluster and crystallize, and the three –BF3− form an anionic pocket, with the Li+ ions solvated by the PEO phase. The high ionic conductivity results from interfacial migration of Li+ ions loosely bonded to three –BF3− anions and the ether oxygens of PEO. Physical crosslinks formed between PEO/Li+ chains and the POSS clusters account for the solid structure of the amorphous PEO matrix. The solid polymer electrolyte has an electrochemical stability window of 4.6 V and excellent interfacial stability with lithium metal.
