BMW has used the IAA 2013 Frankfurt Motor Show to unveil the BMW i8, its plug-in hybrid sports car.Joining the BMW i3 electric car that was launched in July, the BMW i8 is designed to embody the same i values, with an uncompromised drive experience from a car that's firmly looking towards the future.Like the i3, the i8 features a carbonfibre reinforced plastic passenger cell to provide lightweight strength, with the distinctive body panels making up the futuristic external design.But a sports car is more than looks, it's about performance and the BMW i8 has a new plug-in hybrid powertrain. There's a three-cylinder 231hp combustion engine to drive the rear wheels, as well as a 96kW electric motor to drive the front wheels, with lithium-ion batteries.The electric motor provides an acceleration boost to the combustion engine, meaning the BMW i8 will get up to 62mph in 4.4 seconds. There's a limited 155mph top speed from a combined output of 362bhp.These figures might not turn heads in the world of sports cars, but it's achieved with emissions of 59g\/km of CO2 and a stated 113mpg fuel efficiency. You can drive up to 22 miles on the electric motor alone at speeds of up to 75mph and the battery will charge on overrun, as you'd expect from a hybrid. BMW tells us that you can charge the battery to 80 per cent in 2 hours from a mains charger.There are a number of driving modes, from the pure electric through to sports. In the normal "comfort" mode, BMW say you'll get 310 miles from a full petrol tank and fully charged battery. Of course, having a hybrid arrangement, you'll not find yourself facing a lengthy recharging once the battery runs flat.Inside the BMW i8 is futuristic, with a fully digital instrument display and integration with the ConnectedDrive system, so you'll be connected to the world and your smartphone, with all the mod cons.The BMW i8 will be available to order from September 2013, with deliveries expected in July 2014. It will cost \u00a399,845.