Xiaomi, the fast-rising Chinese smartphone maker, is in talks to raise close to $1.5 billion in new capital at a valuation set to exceed $40 billion, in the largest private financing for a venture-backed company since Facebook in 2011. Negotiations with investors including DST– the Russian internet company that also backed Alibaba, Facebook and Airbnb – are yet to be finalized, according to people familiar with the discussions. But if ...