  This study focuses on the development and analysis of a group of high-order
implicit-explicit (IMEX) Runge--Kutta (RK) methods that are suitable for
discretizing gradient flows with nonlinearity that is Lipschitz continuous. We
demonstrate that these IMEX-RK methods can preserve the original energy
dissipation property without any restrictions on the time-step size, thanks to
a stabilization technique. The stabilization constants are solely dependent on
the minimal eigenvalues that result from the Butcher tables of the IMEX-RKs.
Furthermore, we establish a simple framework that can determine whether an
IMEX-RK scheme is capable of preserving the original energy dissipation
property or not. We also present a heuristic convergence analysis based on the
truncation errors. This is the first research to prove that a linear high-order
single-step scheme can ensure the original energy stability unconditionally for
general gradient flows. Additionally, we provide several high-order IMEX-RK
schemes that satisfy the established framework. Notably, we discovered a new
four-stage third-order IMEX-RK scheme that reduces energy. Finally, we provide
numerical examples to demonstrate the stability and accuracy properties of the
proposed methods.
