Cork: Enabler of sustainable and efficient coaxial structural batteries

Structural batteries aim to advance to 'massless' energy storage units. Here we report an electrode-less coaxial battery with a cork-internal shell, CFRP(+)/cork/Cu/Na_2.99Ba_0.005ClO/Al(-), where CFRP is carbon fiber reinforced polymer. The cell may, alternatively, solely have a cork external shell cork/Cu(+)/Na_2.99Ba_0.005ClO/Al(-). Cork is a cellular material with a negative CO₂ footprint, light, elastic, impermeable to gases or liquids, and an excellent thermal insulator. Cork was used tandemly with a CFRP shell, working as the positive current collector to enhance the structural batteries' properties while allowing a giant electrostatic performance in conjunction with the Na⁺ solid-state ferroelectric injected between the Al negative collector and the cork. Cork was shown a polar dielectric. This 'minimalist' cell may perform without copper making the cells even more sustainable. Neither cells contain traditional electrodes, only one or two current collectors. The cells perform from 0 to >50 °C. The maximum capacity of the cork/Cu(+)/Na_2.99Ba_0.005ClO/Al(-) cells is ∼110 mAh.cm^-2 (outer shell) with  ≈ 90 μA cm^-2,  ≈ 0.90 V, V_max ≈ 1.1-1.3 V, I_max ≈ 108 μA cm^-2, and a constant resistance discharging life (>40 days). The novel family of cells presented may also harvest waste heat and thermal energy at a constant temperature as their potential and current increase with temperature. Conversely, rising potentials boost the cells' temperature, as expected from pyroelectrics, as shown herein.