Increase starting speed of acpmdc motor
If the battery is not delivering as much initial current as the motor can tolerate, a capacitor will help. A different battery might also help. If the motor only needs to overcome its own inertia, changing the motor will only help if you can find a motor with a higher ratio of torque to inertia. With a speed of 600 RPM, I suspect the motor includes a speed reduction gear. A gear that is more efficient would help.

To get the maximum rate of acceleration from a given motor, the only answer is the one given by Eugene Sh. "...you will need a controller that has a current controlling loop, providing as much voltage as needed to maintain the maximum allowed current."