HONG KONG — Struggling Internet company Yahoo has secured a lifeline after agreeing to sell half of its prized stake in Chinese e-commerce group Alibaba for about $7.1 billion, with most of the cash going to shareholders.

The deal, announced Sunday in the U.S., will see Alibaba Group buying back half of its 40 percent stake from Yahoo for $6.3 billion cash and up to $800 million of Alibaba preferred shares.

The announcement caps at least a year of rocky on-and-off talks as Yahoo tried to sell the stake as part of efforts to turn around its business. Money from the sale will give Yahoo the financial firepower to return cash to disgruntled shareholders, many of whom are still upset after it squandered an opportunity to sell itself to Microsoft in May 2008 for $33 per share, or $47.5 billion. Yahoo’s stock has sagged since then, trading at $15.42 on Friday.

Yahoo said in a joint statement with Alibaba that it plans to return “substantially all” of the after-tax cash proceeds to shareholders.

The deal, which closes in six months, is good for Yahoo because the company gets a “wad of cash” but still has exposure to fast-growing China, said Napoleon Biggs, head of digital integration at Fleishman-Hillard Asia Pacific.