Natural gas is cheaper, produces less greenhouse emissions, can be ramped up/down quicker, and produces less other toxic emissions (fly ash is horrible stuff) per kWh than coal. It's better in every way than coal. The only reason China is still building coal is because they're China and they don't give a fuck.

re: batteries and mining lithium/cobalt. Sure, mining 1lb of lithium/cobalt isn't any better than mining 1lb of coal, but that 1lb of lithium/cobalt takes you a lot further. You can only burn that 1lb of coal once, but you can cycle that 1lb of lithium/cobalt daily. From a purely environmental standpoint specifically with regards to mining, batteries are still better. However, I don't think the economics are there yet. It will probably be sometime soon though.