Polycyanoacrylate is a very promising matrix for polymer electrolyte, which possesses advantages of strong binding and high electrochemical stability owing to the functional nitrile groups. Herein, a facile and reliable in situ polymerization strategy of poly(ethyl cyanoacrylate) (PECA) based gel polymer electrolytes (GPE) via a high efficient anionic polymerization was introduced consisting of PECA and 4 M LiClO4 in carbonate solvents. The in situ polymerized PECA gel polymer electrolyte achieved an excellent ionic conductivity (2.7 × 10–3 S cm–1) at room temperature, and exhibited a considerable electrochemical stability window up to 4.8 V vs Li/Li+. The LiFePO4/PECA-GPE/Li and LiNi1.5Mn0.5O4/PECA-GPE/Li batteries using this in-situ-polymerized GPE delivered stable charge/discharge profiles, considerable rate capability, and excellent cycling performance. These results demonstrated this reliable in situ polymerization process is a very promising strategy to prepare high performance polymer electrolytes for flexible thin-film batteries, micropower lithium batteries, and deformable lithium batteries for special purpose.Keywords: flexible; in situ polymerization; Li-ion battery; poly(ethyl cyanoacrylate); polymer electrolytes;

Polycarbonate-based polymer electrolytes possess superior ionic conductivity at room temperature, higher lithium ion transference number and wider electrochemical stability window when compared with conventional poly(ethylene oxide)-based polymer electrolytes. Herein, the poly(diethylene glycol carbonate) dimethacrylate macromonomer (PDEC-DMA) was synthesized and the resultant interpenetrating network IPN-PDEC polymer electrolyte was developed via free radical in situ polymerization for polymer electrolyte Li metal batteries. This IPN-PDEC polymer electrolyte exhibited a decent ionic conductivity of 1.64 × 10−4 S cm−1 at room temperature and a wide electrochemical stability window (up to 4.5 V vs. Li+/Li). The LiFePO4/IPN-PDEC/Li and LiFe0.2Mn0.8PO4/IPN-PDEC/Li cells delivered excellent rate capability and cycling performance at room temperature. An all solid state lithium battery was also demonstrated by applying the as-prepared solid polymer electrolyte (SPE-PDEC) at a temperature of 100 °C, which displayed a superior cycling performance. Therefore, the IPN-PDEC network is a promising polymer electrolyte for solid state lithium batteries.

AbstractIt is urgent to seek high performance solid polymer electrolytes (SPEs) via a facile chemistry and simple process. The lithium salts are composed of complex anions that are stabilized by a Lewis acid agent. This Lewis acid can initiate the ring opening polymerization. Herein, a self-catalyzed strategy toward facile synthesis of crosslinked poly(ethylene glycol) diglycidyl ether-based solid polymer electrolyte (C-PEGDE) is presented. It is manifested that the poly(ethylene glycol) diglycidyl ether-based solid polymer electrolyte possesses a superior electrochemical stability window up to 4.5 V versus Li/Li+ and considerable ionic conductivity of 8.9 × 10−5 S cm−1 at ambient temperature. Moreover, the LiFePO4/C-PEGDE/Li batteries deliver stable charge/discharge profiles and considerable rate capability. It is demonstrated that this self-catalyzed strategy can be a very effective approach for high performance solid polymer electrolytes.

The classic poly(ethylene oxide) (PEO) based solid polymer electrolyte suffers from poor ionic conductivity of ambient temperature, low lithium ion transference number and relatively narrow electrochemical window (<4.0 V vs. Li+/Li). Herein, the carbonate-linked PEO solid polymer such as poly(diethylene glycol carbonate) (PDEC) and poly(triethylene glycol carbonate) (PTEC) were explored to find out the feasibility of resolving above issues. It was proven that the optimized ionic conductivity of PTEC based electrolyte reached up to 1.12 × 10−5 S cm−1 at 25 °C with a decent lithium ion transference number of 0.39 and a wide electrochemical window about 4.5 V vs. Li+/Li. In addition, the PTEC based Li/LiFePO4 cell could be reversibly charged and discharged at 0.05 C-rates at ambient temperature. Moreover, the higher voltage Li/LiFe0.2Mn0.8PO4 cell (cutoff voltage 4.35 V) possessed considerable rate capability and excellent cycling performance even at ambient temperature. Therefore, these carbonate-linked PEO electrolytes were demonstrated to be fascinating candidates for the next generation solid state lithium batteries simultaneously with high energy and high safety.Download high-res image (167KB)Download full-size image

Nitrile or cyano-based compounds have aroused interest in high performance battery electrolyte fields due to their unique characteristics such as a high dielectric constant, high anodic oxidization potential and favorable interaction with lithium ions. Particularly, owing to the presence of a unique plastic-crystalline phase, succinonitrile/salt-based solid electrolytes possess an ultra high ionic conductivity of more than 10−3 S cm−1 at room temperature. Herein, recent progress in nitrile-based polymer electrolytes has been reviewed in terms of their potential application in flexible, solid-state or high voltage lithium batteries. Factors affecting the ionic conductivity of nitrile-based electrolytes have also been summarized. We hope that fresh and established researchers can obtain a clear perspective of nitrile based polymer electrolytes and our mini review can spur more extensive interest for the exploration of high performance batteries.

A couple of thermally stable polyborate salts, polymeric lithium pentaerythrite borate (PLPB) and polymeric lithium di(trimethylolpropane)borate (PLDB), for applications in lithium ion batteries were synthesized via a facile one-step reaction in aqueous solution. Both the lithium polyborate salts exhibited a high thermal decomposition temperature at about 240 °C. Besides, their corresponding single-ion dominantly conducting gel polymer electrolytes of ethylene carbonate (EC) and dimethyl carbonate (DMC) (1:1, v/v) swollen PLPB@PVDF-HFP (poly(vinylidenefluoride-co-hexafluoropropene)) and PLDB@PVDF-HFP exhibited favorable ionic conductivity over a wide temperature range, superior electrochemical stability, high lithium ion transference number and Al passivating ability. The Li/LiFePO4 batteries using these single-ion dominantly conducting electrolytes exhibited stable charge–discharge behavior and excellent cycling performance both at room temperature and at elevated temperatures. These superior performances could make this class of gel polymer electrolytes very promising candidates for lithium batteries especially at elevated temperatures.

A heat-resistant and rigid-flexible coupling glass-microfiber nonwoven supported cyanoethyl-β-polyvinyl alcohol composite polymer electrolyte membrane (GFMPE) has been successfully fabricated explored for high-performance lithium batteries. It was demonstrated that the GFMPE possessed enhanced mechanical property, superior dimensional thermostability (>200 °C). In addition, Ethylene carbonate (EC)/Dimethyl carbonate (DMC) solvent soaked GFMPE exhibited a superior Li ion transport number of 0.86, wide electrochemical window up to 4.8 V vs Li+/Li and high ionic conductivity of 0.89 mS/cm at 25 °C. Moreover, LiCoO2/graphite cells using such polymer electrolyte with EC:DMC (1:1, v/v) showed excellent cycling stability and superior rate capability at room temperature. It is important to note that the LiFePO4/Li cell using GFMPE/propylene carbonate (PC) can also operate very well at an elevated temperature of 120 °C. These fascinating results would endow GFMPE a very promising polymer electrolyte in high-performance lithium batteries with improved safety and reliablity.

The LiMn2O4 based lithium batteries using commercially available electrolytes suffer from poor cycling performance at elevated temperatures (above 55 °C). This is mainly caused by the Mn dissolution generated from HF thermally decomposed from the LiPF6 salt at elevated temperatures. In this paper, a single-ion gel polymer electrolyte (polymeric lithium tartaric acid borate @ poly(vinylidene fluoride-co-hexafluoropropylene) was explored for improving the cycling performance of the LiMn2O4 based lithium battery at elevated temperatures owing to superior thermal stability and comparable ionic conductivity. It was manifested that the Li/LiMn2O4 cells using this single-ion gel polymer electrolyte showed stable charge/discharge voltage profiles, preferable rate capability and excellent cycling performance both at room temperature and elevated temperature of 55 °C. The dissolution of metallic Mn in this electrolyte is significantly suppressed than that of LiPF6 electrolyte. These superior performances could endow this single-ion gel polymer electrolyte a promising alternative to the conventional liquid electrolyte system in the LiMn2O4 battery at elevated temperatures.

A novel polymeric lithium tartaric acid borate (PLTB) was synthesized via an one-step reaction in aqueous solution. The polymer electrolyte of PLTB@PVDF-HFP (poly(vinylidene fluoride-co-hexafluoropropene)) was developed by a doctor-blading followed by a soaking process in propylene carbonate (PC). It was manifested that the PC swollen PLTB@PVDF-HFP exhibited excellent electrochemical stability and compatibility with lithium metal electrode, high ionic conductivity and high lithium ion transference number at an operating temperature of 80 °C. The cells using the PC swollen PLTB@PVDF-HFP as electrolyte showed stable charge/discharge profiles, preferable rate capability and satisfactory cycling performance at high temperature. These superior performances of PC swollen PLTB@PVDF-HFP could endow this class of polymer electrolyte a very promising application in lithium batteries operating at relatively high temperature.

Separators possessing thermal stability are highly desired to meet the requirement of application in high power lithium batteries. In this paper, the thermosetting polyimide (PI) nano-fibers based nonwoven separators have been developed by electrospining technique and followed by thermal imidization and mechanical pressing with improved thermal stability and considerable mechanical strength. The high concentration of tortuous nanopores structure and intrinsic chemical configuration lead to good ionic transport and improved electrolyte wettability. The electrochemical characterization at high temperature of 120 °C demonstrates that the LiBOB/PC soaked polyimide nonwovens is an excellent electrolyte system for high temperature operation owing to possessing high oxidative potential, excellent lithium deposition-stripping performance and considerable ionic conductivity. The cells using LiBOB/PC soaked polyimide nonwovens as separator still exhibit stable charge–discharge profiles with quantitative coulumbic efficiency and satisfactory cyclability at 120 °C. The superior electrochemical performance at high temperature could endow these polyimide nonwovens promising alternative to PP separators for high power or high temperature application with superior safety characteristic.Highlights► Polyimide nonwovens show improved thermal stability. ► LiBOB/PC soaked polyimide nonwoven behaves as an electrolyte at 120 °C. ► The cells using polyimide nonwovens can operate at 120 °C.

A couple of thermally stable polyborate salts, polymeric lithium pentaerythrite borate (PLPB) and polymeric lithium di(trimethylolpropane)borate (PLDB), for applications in lithium ion batteries were synthesized via a facile one-step reaction in aqueous solution. Both the lithium polyborate salts exhibited a high thermal decomposition temperature at about 240 °C. Besides, their corresponding single-ion dominantly conducting gel polymer electrolytes of ethylene carbonate (EC) and dimethyl carbonate (DMC) (1:1, v/v) swollen PLPB@PVDF-HFP (poly(vinylidenefluoride-co-hexafluoropropene)) and PLDB@PVDF-HFP exhibited favorable ionic conductivity over a wide temperature range, superior electrochemical stability, high lithium ion transference number and Al passivating ability. The Li/LiFePO4 batteries using these single-ion dominantly conducting electrolytes exhibited stable charge–discharge behavior and excellent cycling performance both at room temperature and at elevated temperatures. These superior performances could make this class of gel polymer electrolytes very promising candidates for lithium batteries especially at elevated temperatures.

Nitrile or cyano-based compounds have aroused interest in high performance battery electrolyte fields due to their unique characteristics such as a high dielectric constant, high anodic oxidization potential and favorable interaction with lithium ions. Particularly, owing to the presence of a unique plastic-crystalline phase, succinonitrile/salt-based solid electrolytes possess an ultra high ionic conductivity of more than 10−3 S cm−1 at room temperature. Herein, recent progress in nitrile-based polymer electrolytes has been reviewed in terms of their potential application in flexible, solid-state or high voltage lithium batteries. Factors affecting the ionic conductivity of nitrile-based electrolytes have also been summarized. We hope that fresh and established researchers can obtain a clear perspective of nitrile based polymer electrolytes and our mini review can spur more extensive interest for the exploration of high performance batteries.

Polycarbonate-based polymer electrolytes possess superior ionic conductivity at room temperature, higher lithium ion transference number and wider electrochemical stability window when compared with conventional poly(ethylene oxide)-based polymer electrolytes. Herein, the poly(diethylene glycol carbonate) dimethacrylate macromonomer (PDEC-DMA) was synthesized and the resultant interpenetrating network IPN-PDEC polymer electrolyte was developed via free radical in situ polymerization for polymer electrolyte Li metal batteries. This IPN-PDEC polymer electrolyte exhibited a decent ionic conductivity of 1.64 × 10−4 S cm−1 at room temperature and a wide electrochemical stability window (up to 4.5 V vs. Li+/Li). The LiFePO4/IPN-PDEC/Li and LiFe0.2Mn0.8PO4/IPN-PDEC/Li cells delivered excellent rate capability and cycling performance at room temperature. An all solid state lithium battery was also demonstrated by applying the as-prepared solid polymer electrolyte (SPE-PDEC) at a temperature of 100 °C, which displayed a superior cycling performance. Therefore, the IPN-PDEC network is a promising polymer electrolyte for solid state lithium batteries.