By Tom Daly and Yilei Sun BEIJING (Reuters) - Contemporary Amperex Technology Co Ltd (CATL), China's biggest maker of batteries for electric vehicles, has begun mass production of high-nickel batteries, its chairman told investors last Friday. The so-called NCM 811 battery, which contains 80 percent nickel, 10 percent cobalt and 10 percent manganese, has a longer lifespan and allows electric vehicles to go further on a single charge, a key point of EV performance. "The company's 811 products are already being mass-produced and the rate of progress will be based on customer demand," CATL Chairman Zeng Yuqun said during an investor question and answer session on April 26, according to a transcript of the session sent to Reuters by the company on Tuesday. Zeng added that CATL, which is building a battery plant in Germany, is expected to further expand battery production capacity in the next two years. CATL said in an internal presentation in August last year that it planned to begin production of the next-generation NCM 811 batteries in 2019. At that time, prices for cobalt were then almost double their current level of $34,500 a tonne. That prompted battery makers to seek to reduce their exposure to cobalt, most of which is mined in the Democratic Republic of Congo, including by switching from a NCM 532 composition in battery cathodes to the high-nickel 811. Delegates at the Fastmarkets Battery Materials conference in Shanghai earlier this month expected the trend toward higher nickel content to continue even with cobalt prices tanking, while securing enough supply of nickel has now become a major concern. Ken Hoffman, leader of the McKinsey EV battery materials research group, told the conference that battery companies and automakers were "petrified about supply." (Reporting by Tom Daly and Yilei Sun in BEIJING; Editing by Brenda Goh and Christian Schmollinger)