Dicationic ionic liquids (DILs) are a fascinating class of novel ionic liquids consisting of two cationic moieties combined with a spacer and two anionic moieties. DILs have recently received more and more attention because of their unique and interesting advantages compared with traditional monocationic ionic liquids while maintaining the same desirable solvation properties, such as higher thermal and chemical stability, excellent structural tunability, superior heat capacity and so on. Given the tunability of DILs, they are more suitable for use in a plethora of science and engineering applications, such as high-temperature organic synthesis, chromatography stationary phases, stable quasi-solid-state dye-sensitized solar cell, separation process, and novel high-temperature lubricant. The recent research progresses of DILs are systematicly reviewed in this paper. General methods for synthesis of various types of DILs, including symmertrical and asymmertrical DILs, are summarized. Properties of DILs in terms of melting point, density, viscosity, heat capacity, thermal stability, surface and interfacial properties, toxicity and biodegradability are respectively described in detail. The structures and molecular dynamics of DILs are introduced in brief. The applications of DILs in organic synthesis, material preparation and electrochemical field are briefly overviewed. In addition, the application prospect and development trend of DILs are finally prospected.

Contents
1 Introduction
2 Synthesis of DILs
2.1 Synthesis of symmertrical DILs
2.2 Synthesis of asymmertrical DILs
3 Properties of DILs
3.1 Physicochemical properties
3.2 Surface & interfacial properties
3.3 Toxicity and biodegradability
4 Structures and molecular dynamics of DILs
4.1 Structures
4.2 Molecular dynamics
5 Applications of DILs
5.1 Organic synthesis
5.2 Material preparation
5.3 Electrochemical field
6 Conclusion