Staples, the Framingham office products company, is ramping up a new “E-Commerce Innovation Center” in Kendall Square in Cambridge. Scheduled to open in May, 2012, the center will house teams responsible for designing and implementing innovative e-commerce solutions for customers who shop Staples stores and websites. The world’s second largest e-commerce company, behind Amazon, Staples is adding IT, product management, usability, and creative positions so it can better reach customers across mobile devices, desktops and stores, the company said.