Lithium ion batteries have high specific energy and lipo have high c rating (high power). Is it possible to put lipo and lithium-ion batteries in parallel if they are at the same voltage and protected by charge control circuitry? This would give you a battery that has high energy density, but can also deliver short bursts of high power. The lipo would charge up from the lithium ion then deliver high power when needed the way capacitors are commonly used. It would be isolated from the circuit by transistors which would control charging and discharging.