General Motors Co on Monday will unveil its next-generation Chevrolet Volt plug-in hybrid and is expected to restate a commitment to build an affordable long-range electric car, doubling down in a segment with scant sales and even skimpier profits. Electric cars and plug-ins like the Volt account for less than 1 percent of the global vehicle market, and falling oil prices are widening the cost gap between electrified cars and petroleum-fueled internal combustion engine vehicles.