Shi Wang

The synthesis of a hyperbranched star polymeric ionic liquid and its application in a polymer electrolyte

This research provides an effective approach to synthesize a hyperbranched star polymeric ionic liquid (HBPS-(PVIMBr)x) with a hyperbranched polystyrene core and poly(1-butyl-3-vinylimidazolium bromide) arms via a combination of atom transfer radical self-condensing vinyl polymerization (ATR-SCVP) and RAFT polymerization. The synthesis process ensures good structural controllability and consistency that all of the arms of the star polymers are ionized. The obtained star polymeric ionic liquid shows good thermal stability with initial thermal decomposition temperatures above 290 °C. Moreover, after anion exchange, the TFSI− anion based hyperbranched star polymeric ionic liquid (HBPS-(PVIMTFSI)x) is used as the all-solid polymer electrolyte for lithium-ion batteries. The electrolytes (HBPS-(PVIMTFSI)x/LiTFSI) fabricated by the solution casting method exhibit a high room temperature ionic conductivity (4.76 × 10−5 S cm−1, the quantitative ratio of LiTFSI to the polymer matrix is 40%), a wide electrochemical window (4.9 V) and great interfacial compatibility.

An ionic liquid crystal-based solid polymer electrolyte with desirable ion-conducting channels for superior performance ambient-temperature lithium batteries

Almost all the traditional ionic liquids lack liquid crystal properties. Only a small number of ionic liquids show liquid crystal properties, which can be named as ionic liquid crystals (ILCs). The liquid crystal characteristics of ILCs endow them with good ordering. More specifically, the ILC macroscopic alignment of phase-segregated ordered nanostructures can be considered as ion pathways and further fixed by photopolymerization to fabricate nanostructured ion-conductive electrolyte films. However, there are no reports using ILC-based solid polymer electrolytes (SPEs) for solid-state polymer lithium batteries (SSPLBs). Here, a free-standing and flexible SPE through photopolymerization of ILC/poly(ethylene glycol) diacrylate/poly(ethylene glycol) dimethyl ether/LiBF4 for SSPLBs was first designed and then successfully prepared. The as-obtained ILC-based SPE exhibits superior comprehensive electrochemical properties in terms of high ionic conductivity (1.96 × 10−4 S cm−1, 30 °C) and a wide electrochemical window (5.2 V). Particularly, the SPE delivers a high transference number of Li+ (0.6) due to the construction of ion channels for efficient transport of Li+. More importantly, the SPE also shows good interface contact with electrodes and can effectively suppress the growth of lithium dendrites. Thus, ILC-based SPE LiFePO4/Li cells present excellent long cycling stability (the average discharge capacity is ∼164 mA h g−1 with coulombic efficiency close to 100% throughout 375 cycles at 0.2 C) and superior rate capability at room temperature. Even at 0 °C, the SSPLBs can run very well. Our study opens a new way for ILC-based SPE to be practically applied in SSPLBs and also provides major progress on addressing the challenges of room temperature/low temperature SSPLBs.

Covalently linked metal–organic framework (MOF)-polymer all-solid-state electrolyte membranes for room temperature high performance lithium batteries

Extensive attention has been paid to metal–organic frameworks (MOFs) in the fields of gas storage/separation, sensors, catalysis, drug delivery and so on. However, the potential application of MOFs as electrolytes in lithium-ion batteries (LIBs) still needs to be further studied. In this study, showcased as the first example in the domain of all-solid-state electrolytes, a MOF covalently linked by flexible polymer chains toward a flexible stand-alone hybrid all-solid-state polymer electrolyte (HSPE) film is prepared by one-pot UV photopolymerization. Specifically, the precursors of the HSPE are composed of vinyl functionalized MOF (M-UiO-66-NH2) nanoparticles, poly(ethylene glycol) diacrylate (PEGDA), a lithium salt and a photoinitiator. It is confirmed that HSPE-1-8 (mM-UiO-66-NH2 : mPEGDA = 1 : 8) possesses over 5 times higher ionic conductivity (4.31 × 10−5 S cm−1 at 30 °C) and much better interfacial contact with Li electrodes than the SPE without incorporation of the vinyl functionalized MOF. Furthermore, at room temperature, the assembled cell of Li/HSPE-1-8/LiFePO4 exhibits outstanding rate capacity (it can reach 140, 124 and 80 mA h g−1 at 0.2, 0.5 and 1C, respectively) and excellent long cycle performance. Meanwhile, the solid cell can also be well run at 60 °C (the discharge capacity reaches 110 mA h g−1 at 2C). Combined with the superior low/high temperature performance of the cell, it is believed that the MOF-based hybrid SPE can be one of the most promising high-safety and high performance electrolytes for LIBs.

High-Performance All-Solid-State Polymer Electrolyte with Controllable Conductivity Pathway Formed by Self-Assembly of Reactive Discogen and Immobilized via a Facile Photopolymerization for a Lithium-Ion Battery

All-solid-state polymer electrolytes (SPEs) have aroused great interests as one of the most promising alternatives for liquid electrolyte in the next-generation high-safety, and flexible lithium-ion batteries. However, some disadvantages of SPEs such as inefficient ion transmission capacity and poor interface stability result in unsatisfactory cyclic performance of the assembled batteries. Especially, the solid cell is hard to be run at room temperature. Herein, a novel and flexible discotic liquid-crystal (DLC)-based cross-linked solid polymer electrolyte (DLCCSPE) with controlled ion-conducting channels is fabricated via a one-pot photopolymerization of oriented reactive discogen, poly(ethylene glycol)diacrylate, and lithium salt. The experimental results indicate that the macroscopic alignment of self-assembled columns in the DLCCSPEs is successfully obtained under annealing and effectively immobilized via the UV photopolymerization. Because of the existence of unique oriented structure in the electrolytes, the prepared DLCCSPE films exhibit higher ionic conductivities and better comprehensive electrochemical properties than the DLCCSPEs without controlled ion-conductive pathways. Especially, the assembled LiFePO4/Li cells with oriented electrolyte show an initial discharge capacity of 164 mA h g-1 at 0.1 C and average specific discharge capacities of 143, 135, and 149 mA h g-1 at the C-rates of 0.5, 1, and 0.2 C, respectively. In addition, the solid cell also shows the first discharge capacity of 124 mA h g-1 (0.2 C) at room temperature. The outstanding cell performance of the oriented DLCCSPE should be originated from the macroscopically oriented and self-assembled DLC, which can form ion-conducting channels. Thus, combining the excellent performance of DLCCSPE and the simple one-pot fabricating process of the DLC-based all-solid-state electrolyte, it is believed that the DLC-based electrolyte can be one of the most promising electrolyte materials for the next-generation high-safety solid lithium-ion batteries.