There are various lightning cables on the market. I ever purchased one but it does not work for iPhone 6…
How to identify a certificated lightning cable that is good for iPhone 6?
Apple has a MFi Program:
Join the MFi licensing program and get the hardware components, tools, documentation, technical support, and certification logos needed to create AirPlay audio accessories and electronic accessories that connect to iPod, iPhone, and iPad.
The easiest way may be to find the MFi logo on the box if the lightning cable.
Examples of MPi logo can be found at https://developer.apple.com/programs/mfi/ .