Gradient-based methods for full-waveform inversion (FWI) have the potential to converge globally but suffer from a slow convergence rate. Newton-type methods provide quadratic convergence, but they are computationally burdensome for large-scale inverse problems. The Hessian-free (HF) optimization method represents an attractive alternative to these above-mentioned optimization methods. At each iteration, the HF approach obtains the search direction by approximately solving the Newton linear system using a conjugate-gradient (CG) algorithm. One issue with HF optimization is that the CG algorithm requires many iterations. In this paper, we develop and compare different preconditioning schemes for the CG algorithm to accelerate the HF Gauss-Newton method. Traditionally, the preconditioners are designed as diagonal Hessian approximations or inverse Hessian approximations. In this research, we propose to construct the l-BFGS inverse Hessian preconditioner with the diagonal Hessian approximations as initial guess. It is shown that the quasi-Newton l-BFGS preconditioning scheme with the pseudo diagonal Gauss-Newton Hessian as initial guess shows the best performances in accelerating the HF Gauss-Newton FWI.