Effect of LiTFSI and LiFSI on Cycling Performance of Lithium Metal Batteries Using Thermoplastic Polyurethane/Halloysite Nanotubes Solid Electrolyte

Abstract

All-solid-state lithium batteries (ASSLB) are promising candidates for next-generation energy storage devices. Nevertheless, the large-scale commercial application of high energy density ASSLB with the polymer electrolyte still faces challenges. In this study, a thin solid polymer composite electrolyte (SPCE) is prepared through a facile and cost-effective strategy with an infiltration of thermoplastic polyurethane (TPU), lithium salt (LiTFSI or LiFSI), and halloysite nanotubes (HNTs) in a porous framework of polyethylene separator (PE) (TPU-HNTs-LiTFSI-PE or TPU-HNTs-LiFSI-PE). The composition, electrochemical performance, and especially the effect of anions (TFSI − and FSI − ) on cycling performance are investigated. The results reveal that the flexible TPU-HNTs-LiTFSI-PE and TPU-HNTs-LiFSI-PE with a thickness of 34 μm exhibit wide electrochemical windows of 4.9 and 5.1 V (vs. Li + /Li) at 60 ℃, respectively. Reduction in FSI − tends to form more LiF and sulfur compounds at the interface between TPU-HNTs-LiFSI-PE and Li metal anode, thus enhancing the interfacial stability. As a result, cell composed of TPU-HNTs-LiFSI-PE exhibits a smaller increase in interfacial resistance of solid electrolyte interphase (SEI) with a distinct decrease in charge-transfer resistance during cycling. Li|Li symmetric cell with TPU-HNTs-LiFSI-PE could keep its stable overpotential profile for nearly 1300 h with a low hysteresis of approximately 39 mV at a current density of 0.1 mA cm −2 , while a sudden voltage rise with internal cell impedance-surge signals was observed within 600 h for cell composed of TPU-HNTs-LiTFSI-PE. The initial capacities of NCM|TPU-HNTs-LiTFSI-PE|Li and NCM|TPU-HNTs-LiFSI-PE|Li cells were 149 and 114 mAh g −1 , with capacity retention rates of 83.52% and 89.99% after 300 cycles at 0.5 C, respectively. This study provides a valuable guideline for designing flexible SPCE, which shows great application prospect in the practice of ASSLB.

Polyacrylonitrile Porous Membrane-Based Gel Polymer Electrolyte by In Situ Free-Radical Polymerization for Stable Li Metal Batteries

“…A large t Li + will reduce the concentration polarization and assist with the performance of LMBs, while a low t Li + will bring about concentration gradients in LMBs and result in a failure of LMBs. 48 By comparing these literatures, it can be found that GPEs applying only a single polymer show a smaller t Li + , while those that used several types of polymers exhibit a t Li + higher than 0.7. Therefore, the simultaneous application of several polymer chains containing different functional groups can promote the transfer efficiency of Li + .…”

“…The t Li + for the PETEA-TCGG-PAN system is 0.77 at 30 °C, higher than that of PETEA-based GPEs in recent reports (Figure S3). A large t Li + will reduce the concentration polarization and assist with the performance of LMBs, while a low t Li + will bring about concentration gradients in LMBs and result in a failure of LMBs . By comparing these literatures, it can be found that GPEs applying only a single polymer show a smaller t Li + , while those that used several types of polymers exhibit a t Li + higher than 0.7.…”

2D Silicate Materials for Composite Polymer Electrolytes

“…Therefore, the space charge effect was formed, and the migration barrier of Li + was effectively decreased, [83] resulting in enhanced ionic conductivity after addition of HNT (Figure 3c-d). [51,84] Besides, compared to ordinary inorganic fillers, layer silicate materials are especially attractive because polymers could intercalate within the silicate layers, which is beneficial to increase the layer spacing and facilitate the ion migration. [59] After modification [72] of sodium montmorillonite (Na-MMT) by a variety of organic modifier agents, the ionic conductivity was significantly enhanced and the value of CPEs modified by quaternary ammonium (MMT-20A) was about triple for those without organic modification.…”

“…The salt anions were adsorbed on the positively charged inner surface; meanwhile, the outer silicon surface tended to adsorb positively charged Li + cations. Therefore, the space charge effect was formed, and the migration barrier of Li + was effectively decreased, [83] resulting in enhanced ionic conductivity after addition of HNT (Figure 3c‐d) [51,84] …”

A MOF-derived hollow Co3O4/NiCo2O4nanohybrid: a novel anode for aqueous lithium ion batteries with high energy density and a wide electrochemical window

“…17 In the charge-discharge test of aqueous LIBs in this voltage range, it is hard to get a large energy density and specific capacity with an unstable electrolyte. In order to enlarge the electrochemical window of aqueous LIBs, lithium bis(trifluoromethane sulfonyl)imide (LiTFSI), [18][19][20][21] an ultra-high concentration aqueous electrolyte whose solubility in water can reach above 20 mol kg −1 at room temperature, could be useful for improving the factor of the electrochemical window. When the concentration of LiTFSI is high enough, the LiTFSI in water can form a "water-in-salt" electrolyte, 22 which can resist hydrolysis and stabilize the battery reaction.…”