Gelation Of Electrolyte Research Articles

Stable Li-Metal Batteries Enabled by in Situ Gelation of an Electrolyte and In-Built Fluorinated Solid Electrolyte Interface.

Lithium-metal batteries (LMBs) are the focus of upcoming energy storage systems with extremely high-energy density. However, the leakage of liquid electrolyte and the uncontrollable dendritic Li growth on the surface of the Li anode lead to their low reversibility and safety risks. Herein, we propose a stable quasi-solid LMB with in situ gelation of liquid electrolyte and an in-built fluorinated solid electrolyte interface (SEI) on the Li anode. The gel polymer electrolyte (GPE) is readily constructed via cationic polymerization between lithium hexafluorophosphate and ether electrolyte. The fluorine-containing additive, fluoroethylene carbonate (FEC), plays a crucial role in the building of a dense SEI with fast interfacial charge transport. The ex situ spectroscopic characterizations suggest that the enhanced LiF species in the SEI with the addition of FEC and the in situ optical microscopy reveal the inhibited dendritic Li growth. Moreover, GPE@FEC exhibits a high oxidative stability beyond 5.0 V (vs Li/Li+). The significantly improved Li plating/stripping efficiency (400 cycles, 98.7%) is presented for the Li∥Cu cells equipped with GPE@FEC. Decent cycling stability is also available for the cells with the LiFePO4 cathode, reflecting the feasibility of GPE@FEC for practical LMBs with enhanced stability and safety.

Gelation of Cathode Electrolytes for Improved Structural Integrity and Enhanced Electrochemical Performance of Li-O2 Batteries

Due to the significantly high theoretical energy density, lithium-oxygen (Li-O2) batteries have been attracting much attention as next generation lithium secondary batteries. Nevertheless, there remain a lot of fundamental challenges to be solved for commercialization of Li-O2 batteries, and the cycling performance of currently reported state-of-the-art Li-O2 batteries is still very poor compared to commercially available Li-ion batteries.[1,2] One of the critical problems for the Li-O2 batteries is the leakage of excess liquid electrolytes from the cathode.[3] During the cell operation, Li2O2 is deposited onto the surface of carbon electrodes, which forces the liquid electrolyte out of the cathode. As a result, the deficiency of liquid electrolytes induces deterioration of the cycling performance. Moreover, the formation of Li2O2 causes serious volume expansion of the carbon cathode, which leads to the structural disintegration of electrodes.[4] To suppress the leakage of electrolytes and disintegration of cathode structures, we are aiming to gelate electrolytes inside the carbon nanotube (CNT) cathodes. Although some gel polymer electrolytes have been reported for Li-O2 batteries so far,[5] gelation of electrolytes inside the cathode has been little investigated. In this study, several types of multi-functional cross-linkers are evaluated to gelate the cathode electrolytes via thermally or UV light-initiated in situ polymerization. By tuning the chemical structure and composition of gelling agents, viscoelastic properties of gels can be broadly controlled. We investigate the effect of gel viscoelasticity and cell restraint pressure on the leakage of electrolyte and mechanical integrity of the CNT cathode, as well as battery performance of the Li-O2 cells. In addition, as another strategy to fabricate CNT-based gel cathodes, solvent-mediated technique is exploited: CNTs, electrolytes, gelling polymers, and volatile solvents are kneaded to form paste films. After evaporation of the solvent, CNT-based gel cathodes were obtained. The relationship between composition and preparation process of the gel cathode and resultant electrochemical performance of Li-O2 cells are studied in detail. We also explore the possibility to reduce the electrolyte amount inside cathodes by gelation toward practically high energy density Li-O2 batteries.

Hybrid high-concentration electrolyte significantly strengthens the practicability of alkaline aluminum-air battery

Alkaline aluminum-air batteries show great potential for energy storage applications because of their high theoretical energy density and low cost. However, they are suffering from severe anodic self-corrosion and the gelation of electrolyte which greatly reduce the practical energy density and shelf life. Herein, we firstly construct an efficient high-energy alkaline Al-air battery based on high-concentration potassium acetate-potassium hydroxide electrolyte and prototype optimization. The self-corrosion of Al anode is greatly suppressed owing to the special hydrate structure in such electrolyte. The Al-air battery with optimum electrolyte demonstrates remarkable increased discharge capacity of 2324 mAh g−1, and the constructed miniaturized Al-air battery enables an outstanding system energy density of 436.1 ​Wh kg−1 (compared with 85.8 ​Wh kg−1 of normal electrolyte) after integrating a discharge product removing system. This work opens up a new direction for the practical realization of high-energy, low-cost, and high-efficiency alkaline Al-air battery and other aqueous metal-air batteries.

Quasi-solid-State Electrolytes for Low-Grade Thermal Energy Harvesting using a Cobalt Redox Couple.

Thermoelectrochemical cells, also known as thermocells, are electrochemical devices for the conversion of thermal energy directly into electricity. They are a promising method for harvesting low-grade waste heat from a variety of different natural and manmade sources. The development of solid- or quasi-solid-state electrolytes for thermocells could address the possible leakage problems of liquid electrolytes and make this technology more applicable for wearable devices. Here, we report the gelation of an organic-solvent-based electrolyte system containing a redox couple for application in thermocell technologies. The effect of gelation of the liquid electrolyte, comprising a cobalt bipyridyl redox couple dissolved in 3-methoxypropionitrile (MPN), on the performance of thermocells was investigated. Polyvinylidene difluoride (PVDF) and poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP) were used for gelation of the electrolyte, and the influence of the different polymers on the mechanical properties was studied. The Seebeck coefficient and diffusivity of the cobalt redox couple were measured in both liquid and gelled electrolytes, and the effect of gelation on the thermocell performance is reported. Finally, the cell performance was further improved by optimizing the concentration of the redox couple and the separation between the hot and cold electrodes, and the stability of the device over 25 h of operation is demonstrated.

In-situ fabrication of macroporous films for dye-sensitised solar cells: formation of the scattering layer and the gelation of electrolytes.

Dye-sensitised solar cells (DSCs) are a promising substitute for conventional silicon solar cells. A scattering layer of submicrometer pores or particles has been widely introduced to achieve a high light-harvesting efficiency. However, many such fabrication processes require high temperatures and multiple steps to prepare the scattering layer. Here, we have developed an in-situ fabrication process for a macroporous (MP) scattering film. The macropores were formed inside the assembled cell via the dissolution of polystyrene (PS) spheres from a PS/TiO2 composite layer caused by exposure to an electrolyte solution. Specifically, the in-situ MP scattering layer decreased the transmittance of the electrode film from 58% to below 1%. The DSCs using these MP scattering layers exhibited an increase in the efficiency of 22%. Moreover, the dissolution of the PS improved the cell stability because of the gelation of the electrolyte solution; the efficiency of the DSCs was maintained at 80% of its initial value after ageing for 20 days, whereas the efficiency of the bare-electrode DSCs was found to have decreased by 50%. We believe that in-situ porous scattering layers show great promise for next-generation flexible DSCs. Moreover, this approach can be extended to various applications that utilize porous film/liquid systems.

A quasi-solid-state dye-sensitized solar cell based on sol–gel derived in situ gelation of a siloxane hybrid electrolyte

A stable dye-sensitized solar cell (DSSC) was fabricated by a novel in situ gelation of the electrolyte. A highly condensed oligosiloxane gel was formed by sol–gel reaction of silane monomers. The oligosiloxane gel DSSC showed reduced charge recombination, and an efficiency of 5.8% with long-term stability.

UV-cross-linked block copolymers for initiator-free, controlled in situ gelation of electrolytes in dye-sensitized solar cells

In this work, a block copolymer as an initiator- and monomer-free UV-cross-linked component for the controlled in situ gelation of electrolytes in dye-sensitized solar cells (DSSCs) is proposed. This block copolymer consists of one block of p-hydroxystyrene units and the other block with poly(ethylene oxide-co-propylene oxide) side chains. This block copolymer is successfully prepared by means of nitroxide-mediated polymerization, imidization reactions and successive hydrolysis reactions. When a homogeneous mixture of this copolymer and a typical liquid electrolyte (LE) is irradiated with UV, the cross-linking is efficient and controlled. The electrolyte in the DSSCs transforms in situ to a gel polymer electrolyte when exposed to UV, affording DSSCs with a relatively high initial solar-to-electricity energy conversion efficiency (η) and improved long-term stability that is significantly greater than that of the DSSCs with LE. These results demonstrate that the electrolyte system containing the UV-cross-linked block copolymer improves the long-term performance of DSSCs and contributes to the development of efficient and stable DSSCs.

In Situ Gelation of Electrolytes for Highly Efficient Gel‐State Dye‐Sensitized Solar Cells

In Situ Gelation of Electrolytes for Highly Efficient Gel‐State Dye‐Sensitized Solar Cells