Photo-Crosslinked Single-Ion Conducting Polymer Electrolyte for Lithium-Metal Batteries

Molecular Mechanisms Driving the Performance of Single-Ion Conducting Polymer Electrolytes in Lithium-Based Batteries

Single-ion conducting polymer electrolytes (SICPEs) hold great potential for the next-generation batteries due to their high safety, fast charging capability, and high energy density. However, their practical application is hindered by the low ionic conductivity (IC). The addition of plasticizers has been shown to effectively enhance IC, although the underlying molecular mechanisms remain unclear. In this study, we employed atomistic molecular dynamics simulations to examine the impact of ethylene carbonate (EC) on lithium-ionic conductivity in a modified polyethylene terephthalate (mPET)-based SICPE. Our simulations reproduced experimental IC values and revealed a similar IC trend with varying EC concentrations, including a notable transition at 50 wt % EC. This enhancement in IC appears to be associated with increased EC diffusion and the preferential coordination of the lithium ions with the oxygen atoms in EC. Analysis of the local oxygen coordination environment around lithium ions further explains the IC transition observed at 50 wt % EC. These findings provide insights into the molecular mechanisms by which EC enhances IC in mPET-based SICPEs, primarily through changes in the local oxygen environment surrounding lithium ions. This study contributes to the design of improved SICPEs with plasticizers, supporting advancements in lithium-ion battery technology.

Robust and Antioxidative Quasi-Solid-State Polymer Electrolytes for Long-Cycling 4.6 V Lithium Metal Batteries

Quasi-solid-state polymer electrolytes (QSPEs) have been considered as one of the most promising electrolytes for high-safety high-energy-density lithium metal batteries (LMBs). However, their inadequate mechanical properties and instability under high voltages pose significant challenges for practical applications. Herein, robust and antioxidative QSPEs are developed based on a polymer-brush-based rigid supporting film (BC-g-PLiMTFSI-b-PPFEMA, BC: bacterial cellulose, PLiMTFSI: poly(lithium (3-methacryloyloxypropylsulfonyl) (trifluoromethylsulfonyl)imide), PPFEMA: poly(2-(perfluorohexyl)ethyl methacrylate)). The robust BC nanofibril backbone can produce a highly porous supporting structure with outstanding mechanical strength. More importantly, the PLiMTFSI-b-PPFEMA side-chains can not only obviously increase the conversion ratio of easily oxidized monomers in QSPEs, but also possess strong interaction with unstable electrolyte components. With such QSPEs as solid-state electrolytes, the Li/LiNi0.8Mn0.1Co0.1O2 full cell with a high cathode loading (20.3 mg cm-2) exhibits a specific discharge capacity of 200.7 mAh g-1 at 0.5 C and demonstrates a long lifespan of 137 cycles with a highly retained capacity of 170.7 mAh g-1 under a cut-off voltage of 4.5 V. More importantly, under a high cut-off voltage of 4.6 V, a high specific capacity of 147.0 mAh g-1 after 187 cycles can be retained for solid-state Li/LiCoO2 cells. This work provides a feasible development strategy of QSPEs for practical long-cycling high-voltage LMBs.

A Zwitterion Coupled All-Solid-State Single Ion Conducting Polymer Electrolyte via Photoinitiated Thiol-Ene Click Polymerization

The all-solid-state single ion conducting polymer electrolyte has a bottleneck in ionic conductivity even though it can prevent concentration polarization. Here, lithium 3,3'-(diallylammonio)bis(propane-1-sulfonyl(trifluoromethyl sulfonyl)imide) (LiDAA(PSI)2) with a symmetrical "one positive, two negative" structure and unsaturated double bonds for propagation, is synthesized. LiDAA(PSI)2 is copolymerized with 1,2-ethanedithiol and poly(ethylene glycol) diacrylate via photoinitiated thiol-ene click polymerization and forms a random copolymer, SPZ for short. For comparison, lithium 3-(diallylamino)propane-1-sulfonyl(trifluoromethyl sulfonyl)imide) (LiDAAPSI) and corresponding copolymer SP are synthesized. The 7Li resonance peak position of LiDAA(PSI)2 shifts to a low-field compared to that of LiDAAPSI, indicating a weaker electrostatic attraction. The symmetrical "one positive, two negative" structure is responsible for the low-field shift, taking effect of charge conjugation. Unsurprisingly, the ionic conductivity of SPZ is 1.69e-5 S cm-1 at 60 °C, which is 1.9 times that of SP. Lithium electroplating and stripping at 0.0125 mA cm-2@0.05 mAh cm-2 at 60 °C are performed. An all-solid-state single ion conducting lithium metal secondary battery is demonstrated. Zwitterion coupled LiDAA(PSI)2 possesses a symmetrical "one positive, two negative" structure, charge conjugation to weaken electrostatic interaction, and unsaturated double bonds for propagation, which inspires the design and synthesis of single ion conducting polymer electrolytes with zwitterion effect.

Diethylenetriaminepentaacetic Acid-based Conducting Solid Polymer Electrolytes Impede Lithium Dendrites and Impart Antioxidant Capacity in Lithium-Ion Batteries

In the development of lithium-ion batteries (LIBs), cheaper and safer solid polymer electrolytes are expected to replace combustible organic liquid electrolytes to meet the larger market demand. However, low ionic conductivity and inadequate cycling stability impede their commercial viability. Herein, a novel flexible conducting solid polymer electrolytes (CSPEs) based on polyvinyl alcohol (PVA) and ion-polarized diethylenetriaminepentaacetic acid (P-DETP) is developed for the first time and applied in LIBs. PVA and P-DETP form a compact polymer network through hydrogen bonding, enhancing the thermomechanical stability of CSPE while restricting the migration of larger anions. Furthermore, density functional theory calculations confirm that P-DETP can facilitate the dissociation of Li+-TFSI- via electrostatic attraction, resulting in increased mobility of lithium ions. Additionally, P-DETP contributes to the formation of a stable electrode-electrolyte interface layer, effectively suppressing the growth of lithium dendrites and improving antioxidant capacity. These synergistic effects enable CSPE to exhibit remarkable properties including high ionic conductivity (2.8 × 10-4 S cm-1), elevated electrochemical potential (5.1 V), and excellent lithium transference number (0.869). Notably, the P-DETP/LiTFSI CSPE demonstrates stable performance not only in LiFePO4 batteries but also adapts to high-nickel ternary LiNi0.88Co0.06Mn0.06O2 cathode, highlighting its immense potential for application in high energy density LIBs.

Progress of Polymer Electrolytes Worked in Solid-State Lithium Batteries for Wide-Temperature Application

Solid-state Li-ion batteries have emerged as the most promising next-generation energy storage systems, offering theoretical advantages such as superior safety and higher energy density. However, polymer-based solid-state Li-ion batteries face challenges across wide temperature ranges. The primary issue lies in the fact that most polymer electrolytes exhibit relatively low ionic conductivity at or below room temperature. This sensitivity to temperature variations poses challenges in operating solid-state lithium batteries at sub-zero temperatures. Moreover, elevated working temperatures lead to polymer shrinkage and deformation, ultimately resulting in battery failure. To address this challenge of polymer-based solid-state batteries, this review presents an overview of various promising polymer electrolyte systems. The review provides insights into the temperature-dependent physical and electrochemical properties of polymers, aiming to expand the temperature range of operation. The review also further summarizes modification strategies for polymer electrolytes suited to diverse temperatures. The final section summarizes the performance of various polymer-based solid-state batteries at different temperatures. Valuable insights and potential future research directions for designing wide-temperature polymer electrolytes are presented based on the differences in battery performance. This information is intended to inspire practical applications of wide-temperature polymer-based solid-state batteries.