To boost the use of electronic devices and driving mileage of electric vehicles, it is urgent to develop lithium-ion batteries (LIBs) with higher energy density and longer life. High-voltage and high-capacity cathode materials, such as LiCoO2, LiNi0.5Mn1.5O4, Ni-rich layered oxides, and lithium-rich layered oxides, are critically important for LIBs to obtain high energy density. Among various forms of these materials, "single-crystal" cathodes (SCCs) have shown many advantages over other forms for industrial applications, including good crystallinity, high mechanical strength, high reaction homogeneity, small specific surface area, excellent structural stability, and high thermal stability, which can noticeably improve the cycling performance and safety of SCC-based batteries. Therefore, SCCs have received wide attention from academic to industrial communities and have been applied to the liquid-based and solid-state batteries in recent years. In this paper, the advantages, progress, and challenges of SCCs for high-voltage cathode materials are reviewed. Moreover, we summarize the efforts for improving the electrochemical performance of SCCs, intending to provide insights into the development of high-performance cathodes for practical LIBs.