Li-ion conductivity in PEO-graphene oxide nanocomposite polymer electrolytes: A study on effect of the counter anion

Graphene in Solid-State Batteries: An Overview

Solid-state batteries (SSBs) have emerged as a potential alternative to conventional Li-ion batteries (LIBs) since they are safer and offer higher energy density. Despite the hype, SSBs are yet to surpass their liquid counterparts in terms of electrochemical performance. This is mainly due to challenges at both the materials and cell integration levels. Various strategies have been devised to address the issue of SSBs. In this review, we have explored the role of graphene-based materials (GBM) in enhancing the electrochemical performance of SSBs. We have covered each individual component of an SSB (electrolyte, cathode, anode, and interface) and highlighted the approaches using GBMs to achieve stable and better performance. The recent literature shows that GBMs impart stability to SSBs by improving Li+ ion kinetics in the electrodes, electrolyte and at the interfaces. Furthermore, they improve the mechanical and thermal properties of the polymer and ceramic solid-state electrolytes (SSEs). Overall, the enhancements endowed by GBMs will address the challenges that are stunting the proliferation of SSBs.

Graphene Oxide Aerogel Foam Constructed All-Solid Electrolyte Membranes for Lithium Batteries

With the development of electric vehicles and products, lithium metal batteries with solid-state electrolytes have shown a broad application prospect. However, the uneven deposition of lithium, low ion conductivity, narrow electrochemical window, and high interfacial impedance limit the safety and performance of the solid-state batteries. Herein, we develop a non-ceramic solid electrolyte based on the graphene oxide aerogel frame filling with polyethylene oxide (GSPE). The resulting uniform and resilient framework structure form a continuous Li-ion adsorption zone, which ensures uniform ion-current distribution at the interface while obtaining the relatively high ionic conductivity, effectively preventing the uneven deposition of lithium, and thus greatly improving the battery stability. Comprehensive electrochemical analysis showed that GSPE achieved an ionic conductivity of 4.12 × 10^-4 S cm^-1 at 50 °C. The assembled LiFePO₄(LFP) |GSPE| Li full battery can stably cycle for more than 100 cycles at 0.1 C, and the lithium symmetrical battery can continuously be plating-peeling for more than 600 h at 0.1 mA cm^-2. The method of using the carbon aerogel structure to achieve the uniform deposition of lithium ions has explored a new possible research direction for all-solid-state batteries.

Hydroxyapatite Nanowire-Reinforced Poly(ethylene oxide)-Based Polymer Solid Electrolyte for Application in High-Temperature Lithium Batteries

Hybrid polymer electrolytes with excellent performance at high temperatures are very promising for developing solid-state lithium batteries for high-temperature applications. Herein, we use a self-supporting hydroxyapatite (HAP) nanowire membrane as a filler to improve the performance of a poly(ethylene oxide) (PEO)-based solid-state electrolyte. The HAP membrane could comprehensively improve the properties of the hybrid polymer electrolyte, including the higher room-temperature ionic conductivity of 1.05 × 10^-5 S cm^-1, broad electrochemical windows of up to 5.9 V at 60 °C and 4.9 V at 160 °C, and a high lithium-ion migration of 0.69. In addition, the LiFePO₄//Li full battery with a solid electrolyte possesses good rate capability, cycling, and Coulomb efficiency at extreme high temperatures, that is, after 300 continuous charge and discharge cycles at 4 C rate, the discharge capacity retention rate is 77% and the Coulomb efficiency is 99%. The use of the flexible self-supporting HAP nanowire membrane to improve the PEO-based solid composite electrolyte provides new strategies and opportunities for developing rechargeable lithium batteries in extreme high-temperature applications.

Ion Liquid Modified GO Filler to Improve the Performance of Polymer Electrolytes for Li Metal Batteries

Polymer electrolytes for Li metal batteries (LMBs) should be modified to improve their ionic conductivity and stability against the lithium electrode. In this study, graphene oxide (GO) was modified by ion liquid (IL), and the IL modified GO (GO-IL) had been used as a filler for polyethylene oxide (PEO). The obtained solid polymer electrolyte (SPE) is of high ionic conductivity, low crystallinity and excellent stability against the lithium electrode. The PEO/GO-IL was characterized by various techniques, and its structure and performance were analyzed in detail. By addition of 1% GO-IL, the ionic conductivity of the PEO/GO-IL SPE reaches 1.8 × 10-5 S cm-1 at 25°C, which is 10 times higher than PEO (1.7 × 10-6 S cm-1), and the current density for stable Li plating/stripping in PEO/GO-IL can be increased to 100 μA cm-2 at 60°C. LiFePO4/Li cell (using PEO/GO-IL SPE) tests indicated that the initial discharge capacity can reach ~145 mA h g-1 and capacity retention can maintain 88% even after 100 cycles at a rate of 0.1C and at 60°C. Our creative work could provide a useful method to develop SPEs with excellent performance, thus accelerating the commercial application of LMBs.

Hybrid Solid Polymer Electrolytes with Two-Dimensional Inorganic Nanofillers

Solid polymer electrolytes are of rapidly increasing importance for the research and development of future safe batteries with high energy density. The diversified chemistry and structures of polymers allow the utilization of a wide range of soft structures for all-polymer solid-state electrolytes. With equal importance is the hybrid solid-state electrolytes consisting of both "soft" polymeric structure and "hard" inorganic nanofillers. The recent emergence of the re-discovery of many two-dimensional layered materials has stimulated the booming of advanced research in energy storage fields, such as batteries, supercapacitors, and fuel cells. Of special interest is the mass transport properties of these 2D nanostructures for water, gas, or ions. This review aims at the current progress and prospective development of hybrid polymer-inorganic solid electrolytes based on important 2D materials, including natural clay and synthetic lamellar structures. The ion conduction mechanism and the fabrication, property and device performance of these hybrid solid electrolytes will be discussed.