* Nissan relies on CHAdeMO charging standard (Adds executive comments): HAGEN, Germany (Reuters) - Nissan’s Leaf became the first electric vehicle (EV) to secure regulatory approval as an energy backstop for Germany’s electricity grid, the Japanese carmaker said on Tuesday, something it hopes will attract corporate fleet customers. So-called vehicle-to-grid (V2G) technology is a connection between the EV and the grid through which power can flow from the grid to the vehicle and vice-versa. That potentially enables car owners to sell energy to the network, while utilities could use electric cars as a backstop if demand rises.