Here we show that through a straightforward synthesis it is possible to create a bulk material, Na0.35MnO2, with isolated sheets. Due to such an arrangement of the oxide layers, this ionic conductor was found to be genuinely pseudocapacitive, with charge storage not limited by diffusion of ions between stacked layers, resulting in capacitance values of 190 F g−1 under exceptionally high current rates of up to 200 A g−1.

Here we show that through a straightforward synthesis it is possible to create a bulk material, Na0.35MnO2, with isolated sheets. Due to such an arrangement of the oxide layers, this ionic conductor was found to be genuinely pseudocapacitive, with charge storage not limited by diffusion of ions between stacked layers, resulting in capacitance values of 190 F g−1 under exceptionally high current rates of up to 200 A g−1.