Solid-state electrolytes are attracting increasing interest for electrochemical energy storage technologies. In this Review, we provide a background overview and discuss the state of the art, ion-transport mechanisms and fundamental properties of solid-state electrolyte materials of interest for energy storage applications. We focus on recent advances in various classes of battery chemistries and systems that are enabled by solid electrolytes, including all-solid-state lithium-ion batteries and emerging solid-electrolyte lithium batteries that feature cathodes with liquid or gaseous active materials (for example, lithium–air, lithium–sulfur and lithium–bromine systems). A low-cost, safe, aqueous electrochemical energy storage concept with a ‘mediator-ion’ solid electrolyte is also discussed. Advanced battery systems based on solid electrolytes would revitalize the rechargeable battery field because of their safety, excellent stability, long cycle lives and low cost. However, great effort will be needed to implement solid-electrolyte batteries as viable energy storage systems. In this context, we discuss the main issues that must be addressed, such as achieving acceptable ionic conductivity, electrochemical stability and mechanical properties of the solid electrolytes, as well as a compatible electrolyte/electrode interface. This Review details recent advances in battery chemistries and systems enabled by solid electrolytes, including all-solid-state lithium-ion, lithium–air, lithium–sulfur and lithium–bromine batteries, as well as an aqueous battery concept with a mediator-ion solid electrolyte.

Lithium battery chemistries enabled by solid-state electrolytes

Metal Oxides and Oxysalts as Anode Materials for Li Ion Batteries

Electrolytes have been identified as some of the most influential components in the performance of electrochemical supercapacitors (ESs), which include: electrical double-layer capacitors, pseudocapacitors and hybrid supercapacitors. This paper reviews recent progress in the research and development of ES electrolytes. The electrolytes are classified into several categories, including: aqueous, organic, ionic liquids, solid-state or quasi-solid-state, as well as redox-active electrolytes. Effects of electrolyte properties on ES performance are discussed in detail. The principles and methods of designing and optimizing electrolytes for ES performance and application are highlighted through a comprehensive analysis of the literature. Interaction among the electrolytes, electro-active materials and inactive components (current collectors, binders, and separators) is discussed. The challenges in producing high-performing electrolytes are analyzed. Several possible research directions to overcome these challenges are proposed for future efforts, with the main aim of improving ESs' energy density without sacrificing existing advantages (e.g., a high power density and a long cycle-life) (507 references).

A review of electrolyte materials and compositions for electrochemical supercapacitors

Notably, many significant breakthroughs for a new generation of supercapacitors have been reported in recent years, related to theoretical understanding, material synthesis and device designs. Herein, we summarize the state-of-the-art progress toward mechanisms, new materials, and novel device designs for supercapacitors. Firstly, fundamental understanding of the mechanism is mainly focused on the relationship between the structural properties of electrode materials and their electrochemical performances based on some in situ characterization techniques and simulations. Secondly, some emerging electrode materials are discussed, including metal–organic frameworks (MOFs), covalent organic frameworks (COFs), MXenes, metal nitrides, black phosphorus, LaMnO3, and RbAg4I5/graphite. Thirdly, the device innovations for the next generation of supercapacitors are provided successively, mainly emphasizing flow supercapacitors, alternating current (AC) line-filtering supercapacitors, redox electrolyte enhanced supercapacitors, metal ion hybrid supercapacitors, micro-supercapacitors (fiber, plane and three-dimensional) and multifunctional supercapacitors including electrochromic supercapacitors, self-healing supercapacitors, piezoelectric supercapacitors, shape-memory supercapacitors, thermal self-protective supercapacitors, thermal self-charging supercapacitors, and photo self-charging supercapacitors. Finally, the future developments and key technical challenges are highlighted regarding further research in this thriving field.

Latest advances in supercapacitors: from new electrode materials to novel device designs.

Lithium-sulfur (Li-S) batteries have attracted tremendous interest because of their high theoretical energy density and cost effectiveness. The target of Li-S battery research is to produce batteries with a high useful energy density that at least outperforms state-of-the-art lithium-ion batteries. However, due to an intrinsic gap between fundamental research and practical applications, the outstanding electrochemical results obtained in most Li-S battery studies indeed correspond to low useful energy densities and are not really suitable for practical requirements. The Li-S battery is a complex device and its useful energy density is determined by a number of design parameters, most of which are often ignored, leading to the failure to meet commercial requirements. The purpose of this review is to discuss how to pave the way for reliable Li-S batteries. First, the current research status of Li-S batteries is briefly reviewed based on statistical information obtained from literature. This includes an analysis of how the various parameters influence the useful energy density and a summary of existing problems in the current Li-S battery research. Possible solutions and some concerns regarding the construction of reliable Li-S batteries are comprehensively discussed. Finally, insights are offered on the future directions and prospects in Li-S battery field.

More Reliable Lithium-Sulfur Batteries: Status, Solutions and Prospects.

The fabrication of flexible, stretchable and rechargeable devices with a high energy density is critical for next-generation electronics. Herein, fiber-shaped Zn-air batteries, are realized for the first time by designing aligned, cross-stacked and porous carbon nanotube sheets simultaneously that behave as a gas diffusion layer, a catalyst layer, and a current collector. The combined remarkable electronic and mechanical properties of the aligned carbon nanotube sheets endow good electrochemical properties. They display excellent discharge and charge performances at a high current density of 2 A g(-1) . They are also flexible and stretchable, which is particularly promising to power portable and wearable electronic devices.

Flexible, Stretchable, and Rechargeable Fiber-Shaped Zinc-Air Battery Based on Cross-Stacked Carbon Nanotube Sheets.

Portable and multifunctional electronic devices are developing in the trend of being small, flexible, roll-up, and even wearable, which asks us to develop flexible and micro-sized energy conversion/storage devices. Here, the high performance of a flexible, wire-shaped, and solid-state micro-supercapacitor, which is prepared by twisting a Ni(OH)2-nanowire fiber-electrode and an ordered mesoporous carbon fiber-electrode together with a polymer electrolyte, is demonstrated. This micro-supercapacitor displays a high specific capacitance of 6.67 mF cm-1 (or 35.67 mF cm-2) and a high specific energy density of 0.01 mWh cm-2 (or 2.16 mWh cm-3), which are about 10-100 times higher than previous reports. Furthermore, its capacitance retention is 70% over 10 000 cycles, indicating perfect cyclic ability. Two wire-shaped micro-supercapacitors (0.6 mm in diameter, approximate to 3 cm in length) in series can successfully operate a red light-emitting-diode, indicating promising practical application. Furthermore, synchrotron radiation X-ray computed microtomography technology is employed to investigate inner structure of the micro-device, confirming its solid-state characteristic. This micro-supercapacitor may bring new design opportunities of device configuration for energy-storage devices in the future wearable electronic area.

Flexible and Wire-Shaped Micro-Supercapacitor Based on Ni(OH)2-Nanowire and Ordered Mesoporous Carbon Electrodes

Three-dimensional ordered mesoporous/macroporous carbon sphere arrays (MMCSAs) are synthesized and then used as a catalyst for Li-O2 batteries. The hierarchical porous structure of the MMCSAs not only facilitates electrolyte immersion and Li(+) diffusion but also provides an effective space for O2 diffusion and O2 /Li2 O2 conversion, and thus efficiently improves the performance of Li-O2 batteries.

Ordered hierarchical mesoporous/macroporous carbon: a high-performance catalyst for rechargeable Li-O(2) batteries.

Metal-organic frameworks (MOFs) with open metal sites enrich the population of O2 in the pores significantly and assist the Li-O2 reaction when employed as a cell electrode material. A primary capacity of 9420 mA h g(-1) is achieved in a cell with Mn-MOF-74; more than four times higher than the value obtained in a cell without an MOF.

Ziyang Guo

Papers

Flexible, Stretchable, and Rechargeable Fiber-Shaped Zinc-Air Battery Based on Cross-Stacked Carbon Nanotube Sheets.

Flexible and Wire-Shaped Micro-Supercapacitor Based on Ni(OH)2-Nanowire and Ordered Mesoporous Carbon Electrodes

Ordered hierarchical mesoporous/macroporous carbon: a high-performance catalyst for rechargeable Li-O(2) batteries.

Metal–Organic Frameworks as Cathode Materials for Li–O2 Batteries

Organic Batteries Operated at −70°C