OptimumNano Energy Co., China's third-largest battery maker for electric vehicles, disclosed last week it will suspend battery cell production for six months. The Shenzhen-listed company, which is using less than 23 percent of its production capacity, is far from the only Chinese battery maker in trouble. Burdened with underused plants, dozens of EV battery suppliers have gone out of business in China since 2015. And more likely will meet the same fate down the road. Beijing started offering generous subsidies for EVs in 2009 in the hope that domestic automakers and suppliers could become world-class players in the EV market. EV output has increased substantially across China. Last year, production of electrified vehicles, most of which were battery EVs, jumped 54 percent to approach 800,000. Manufacturing capacity for EV batteries has also surged in tandem. By the end of 2017, combined annual capacity of EV battery makers in China topped 200 gigawatt-hours, double the tally a year earlier.