Ensure that Fast Charging is enabled in settings. To do so you must go to Settings>Power Saving> Fast Charge and make sure it is checked. If that doesn't work then clean out the charging port. If that still doesn't work then try another cable. The cable should be thicker in shielding. Ensure the cable isn't frayed, bent or damaged in any way. I find in my own experience that charging cables over 3 feet long tend to be shoddy at fast charging. Ensure your charger brick actually works by charging another device.