Here's something I've been using in my own esp8266 projects for a while, LiFePo4 18650 cells. Their working voltage range, 2.6 - 3.6, 3.2v typical, makes them perfect for esp chips, and you remove the quiescent drain (though really low for mcp1700). Downsides of LFP being, lower capacity in the same size (energy density), pouch cells are generally not available and LiIon is a far more mature tech, with easy (and cheap tp/tc 4056) charging solutions.
Here's something I've been using in my own esp8266 projects for a while, LiFePo4 18650 cells. Their working voltage range, 2.6 - 3.6, 3.2v typical, makes them perfect for esp chips, and you remove the quiescent drain (though really low for mcp1700). Downsides of LFP being, lower capacity in the same size (energy density), pouch cells are generally not available and LiIon is a far more mature tech, with easy (and cheap tp/tc 4056) charging solutions.