Allen & Overy (A&O) Tokyo managing partner and former managing partner contender Simon Black has left after 25 years at the firm.

Black has joined the management of BESS, a startup that operates storage facilities for large-scale batteries in the UK, according to a post by Black on his LinkedIn page.

In the post, he added that he is one of the founding shareholders of the business, and that he plans to divide his time between BESS and a legal and technology consulting business.

He stepped down as A&O Tokyo head at the end of June and retired from the partnership last month.

Energy and infrastructure projects partner Matthias Voss, who currently splits his time between Seoul and Tokyo, has replaced him as Tokyo head.

Black emerged in late 2015 as one of the four candidates in the running for the global managing partner role at A&O. He lost out to former global corporate co-head Andrew Ballheimer, who took over in May 2016, replacing Wim Dejonghe who became senior partner. Black was also up against banking co-head Andrew Trahair and London banking partner Michael Castle.

A finance lawyer, Black has advised lenders and investors on energy and infrastructure projects across Asia. Earlier this year, he advised Japanese energy investor Jera on a $200m (£152m) investment in India's ReNew Power Ventures.

Black took over as Tokyo managing partner at A&O in 2013, following predecessor Aled Davies' departure to Milbank, Tweed, Hadley & McCloy.

Having joined the firm in London in 1992, Black spent most of his career at the firm's Asian offices, both in China and Japan. Before moving back to Tokyo in 2010, he was managing partner of the firm's Beijing and Shanghai offices.

His exit leaves A&O with 21 lawyers in Tokyo, including four partners.

A&O said: "Simon Black has retired from Allen & Overy. We would like to thank him for the contribution he has made during his time at the firm and wish him all the best for the future."