Help With Adafruit Motor Shield V2 Driving DC Fans.

I am trying to drive a small 12V DC Fan using an Arduino Uno and the Adafruit Motor Shield V2 powered by a 12V lithium battery. Here is the link for the fan:

I am simply trying to control the speed of the fan using the DC output on the motor driver. However, the fan itself refuses to spin at anything less than +12V.

I can power the fan using another DC voltage source such as a 9V battery, but can't seem to use the AFMS to adjust the speed of the fan.

Any suggestions?