A gel single ion conducting polymer electrolyte enables durable and safe lithium ion batteries via graft polymerization

Abstract

A post-grafting strategy to synthesize single ion conducting polymer electrolytes for lithium metal secondary batteries.

Small Groups, Big Impact: Eliminating Li+ Traps in Single-Ion Conducting Polymer Electrolytes

“…All considered PVdF-HFP blended SIPE membranes exhibit different polymer architectures, solvent solutions, and membrane compositions (other major characteristics of the polymer blends are collected in Table S1 , see Supplemental Information ) ( Zhang et al., 2014a ; Sun et al., 2014 ; Zhang et al., 2014b ; Qin et al., 2015 ; Rohan et al., 2015 ; Liu et al., 2016 ; Pan et al., 2016 ; Zhang et al., 2017a , 2017b ; Dong et al., 2018 ; Li et al., 2018 ; Chen et al., 2018 ; Li et al., 2019 ). The obtained morphologies of polymer electrolyte membranes similarly prepared from solution casting varied from highly porous (micrometer-sized pores) ( Sun et al., 2014 ; Zhang et al., 2014a , 2014b ; Pan et al., 2015 , 2016 ; Rohan et al., 2015 ; Zhang et al., 2017a , 2017b , 2018 ; Dong et al., 2018 ; Chen et al., 2018 ; Li et al., 2019 ) to rather dense structures (nanometer-sized pores), ( Zhang et al., 2014a , 2014b ; Qin et al., 2015 ; Liu et al., 2016 ; Pan et al., 2016 ; Li et al., 2018 ; Borzutzki et al., 2019 ), with no clear trend for different SIPE structures. Note, though, that a homogeneous membrane morphology is considered beneficial to prevent the formation of inhomogeneous high-surface-area (“needle-like” or “dendritic”) lithium (HSAL [ Winter et al., 2018 ]) deposits that otherwise could grow throughout the pore structures, eventually yielding short circuits within the cells ( Zhang, 2018 ; Lagadec et al., 2019 ).…”

“…This is in contrast to gel-type polymer electrolytes that might incorporate up to 2,200 wt % of plasticizer(s) ( Zhang et al., 2018 ; Zhong et al., 2019 ; Zhou et al., 2019 ). To date, merely a few quasi-solid SIPEs with a room temperature (RT) ionic conductivity of 1 mS cm −1 or higher are reported ( Deng et al., 2017 ; Oh et al., 2016 ; Rohan et al., 2014 ), whereas other plasticized SIPE material classes including block copolymers( Nguyen et al., 2018 ) or blend-type compounds( Zhang et al., 2014a ; Sun et al., 2014 ; Zhang et al., 2014b ; Qin et al., 2015 ; Rohan et al., 2015 ; Liu et al., 2016 ; Pan et al., 2016 ; Zhang et al., 2017a , 2017b ; Dong et al., 2018 ; Li et al., 2018 ; Chen et al., 2018 ; Li et al., 2019 ) do not accomplish ionic conductivities of more than 1 mS cm −1 . However, in case of poly(vinylidene difluoride- co -hexafluoropropylene) (PVdF-HFP) blended SIPE membranes (the materials class investigated in this work), several promising single ion conducting polymer structures were explored, considering variations of the anionic species attached to polymer backbone or side chains, the ratio of the blend constituents, the nature of plasticizer molecules, as well as concepts for membrane fabrication and solvent uptake ( Table S1 ) ( Sun et al., 2014 ; Zhang et al., 2014a , 2014b ; Pan et al., 2015 , 2016 ; Liu et al., 2016 ; Zhang et al., 2017a , 2017b , 2018 ; Dong et al., 2018 ; Li et al., 2019 ).…”

Reinforce the Adhesion of Gel Electrolyte to Electrode and the Interfacial Charge Transfer via In Situ Electrospinning the Polymeric Nanofiber Matrix

“…Indeed, as compared in Table S1, Supporting Information, the overall electrochemical performances of the LiFePO 4 half coin cell using i-PVdF-HFP gel electrolyte prepared in the work are comparable with those using the PVdF-HFP-based gel electrolyte fabricated through doctor blade, electrophoretic deposition, solution casting, and others reported so far. [33][34][35][36][37][38][39][40][41] To get insight into the interfacial structural variations of the gel electrolytes and LiFePO 4 electrodes after the charge/ discharge cycling, the half coin cells were disassembled after being charged/discharged for 500 cycles. The SEM images ( Figure 6) of the LiFePO 4 electrode after the i-PVdF-HFP gel electrolyte was peeled off clearly show that there are still a few PVdF-HFP nanofiber left on the LiFePO 4 electrode, but almost no PVdF-HFP nanofibers are observed after the f-PVdF-HFP gel electrolyte was removed.…”

Polymers in Lithium‐Ion and Lithium Metal Batteries

“…Modifying anion groups that contain strong electronwithdrawing groups on polymers is one common method. Generally, sulfoacid (SO 3 − ), [110] sulfimide (SO 2 N − R), [111] borate (BO 4 − ), [112,113] and carboxylic acid (COO − ) [114] are commonly used anions. Covalent linkage between anion groups and the polymer main chain keeps anion parts fixed while Li + cations are able to move freely.…”