A Starbucks Corp. store in Shanghai, China.Qilai Shen/BloombergStarbucks has agreed to sell an up to 60% slice in its China business to Chinese investment firm Boyu Capital in a deal that values the operation at $4 billion.The Seattle-based company announced on Monday that it has formed a joint venture in China with Boyu. The investment firm will own up to 60% in the new entity, while Starbucks retains a 40% interest and keeps the right to license the brand. The total value of its China retail business exce ...