Electrolytes have played critical roles in electrochemical energy storage. In Li-ion battery, liquid electrolytes have shown their excellent performances over decades, such as high ionic conductivity (∼10–3 S cm–1) and good contacts with electrodes. However, the use of liquid electrolytes often brought risks associated with leakage and combustion of organic electrolytes. Hence, polymer electrolytes become potential candidates to replace liquid electrolyte systems. Although solid polymer electrolytes (SPEs) offer better safety and good mechanical properties to take over liquid electrolytes, most of them only deliver low ionic conductivities (∼10–8 S cm–1) and poor contact with electrodes, resulting in poor cycle performance and low electrical capacity of the batteries. In addition, gel polymer electrolytes (GPEs) have received increasing research attention due to their relevant characteristics, which extend from liquid electrolytes and solid polymer electrolytes. In this review, state-of-the-art samples of gel polymer electrolytes are elucidated with respect to their structural design and electrochemical properties to determine their application potential in Li-ion batteries (LIBs). First, we present the general requirements of GPEs for LIBs applications, followed by important electrochemical properties of GPEs for LIBs including ionic conductivity, transference number, and ionic transport mechanisms. Furthermore, recent progress of common polymers, namely, polyether, polyvinyl, polynitrile, polycarbonate, and polyacrylate, as polymer host of GPEs has been carefully explained. Finally, the alternative polymers were also discussed to provide new approaches for further developments of GPEs to fulfill the demanded properties for practical applications.

Aromatic polyimide (PI) derivatives have recently been investigated as redox-active electrode materials for Li-ion batteries because of their high thermal stability and thermo-oxidative stability complemented by excellent solvent resistance, good electrical and mechanical properties, and chemical resistance. In this work, we report two PI derivatives from a newly synthesized 4,4′-diamino-3″,4″-dicyanotriphenylamine (DiCN-TPA) monomer and two dianhydrides, pyromellitic dianhydride (PMDA) and 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA); designated as TPA-PMPI and TPA-NTCPI, respectively, as electrode materials for Li-ion batteries. Characterizations of the PIs reveal excellent thermal stability and bipolar property. The incorporation of DiCN-TPA into the polymer structure resulted to a disordered chain arrangement, thus giving high glass transition temperatures (T g). Electrochemical performance tests reveal that TPA-NTCPI cathode delivered a reversible specific capacity of 150 mAh g–1 at 0.1 A g–1 and exhibited a stability up to 1000 cycles. On the other hand, TPA-PMPI anode delivered a high specific capacity of up to 1600 mAh g–1 at 0.1 A g–1 after 100 cycles. The electrochemical performance of TPA-NTCPI cathode and TPA-PMPI anode are both among the best compared with other reported aromatic PI-based electrodes. The long cycle lifetime and excellent battery performance further suggest that TPA-NTCPI and TPA-PMPI are promising organic electrode materials for next generation Li-ion batteries.

Multifunctional energy storage devices show great promise in reducing the size and volume of devices, improving the storage capacity, and minimizing the cost in materials and fabrication while bringing the...