Preserving high energy densities of batteries at fast charge and discharge rates at the cell-stack level is a critical challenge for applications such as electric vehicles. Current manufacturing methods usually produce lithium (Li) ion battery electrodes <100 μm thin with unavoidable tortuous internal porosity that reduces energy densities at fast rates. Here, we use ice templating to manufacture ultra-thick (900 μm) LiFePO₄-based cathodes containing fast ion transport pathways and a pore structure gradient through the electrode thickness that promote high energy densities at fast rates. The electrodes exhibit 94 mA h g⁻¹ at an ultra-high current density of 15 mA cm⁻² (67% higher gravimetric energy density at the cell-stack level including inactive components) compared with 47 mA h g⁻¹ for conventional electrodes containing random structures and the same materials. X-ray computed tomography and modeling are used to quantify the electrode structure within different sub-domains and along orthogonal directions, which directly rationalizes the excellent dynamic performance. The electrode microstructure design, manufacturing method and characterization tools will be of use for other energy storage and conversion devices that rely on fast directional mass transport.

Thick electrodes (>500 μm) that minimize the proportion of inactive components (current collectors, separators, etc.) are attractive for high energy density lithium ion battery (LIB) cell-stacks. However, the tortuous porosity inside the electrodes usually restricts the use of these more cost-effective thick electrodes, because lithium ion diffusion becomes restricted and capacity reduces to impractical levels. To overcome this problem, we manufacture 900 μm thick cathodes with aligned pore arrays in the predominant ion transport direction using a scalable ice templating technique without the need for post-processing sintering. The aligned porosity combined with a coral-like electrode structure exhibited high areal and gravimetric capacities (14 mA h cm⁻² and 142 mA h g⁻¹ at 0.1C) as well as a sustained rate capability at faster (dis)charge rates (e.g. 12 mA h cm⁻² and 124 mA h g⁻¹ at 1C) that outperformed the capacities (0.5 mA h cm⁻² and 141 mA h g⁻¹ at 0.1C) and rate capability (e.g. 0.4 mA h cm⁻² and 103 mA h g⁻¹ at 1C) of conventional LIB electrodes containing the same materials and with a random microstructure fabricated by standard slurry casting. X-ray tomography and numerical modelling were used to quantify and confirm the aligned porosity benefits, which were preserved after many cycles of operation, along with robust mechanical integrity of the electrodes.

Supercapacitors are in demand for short-term electrical charge and discharge applications. Unlike conventional supercapacitors, solid-state versions have no liquid electrolyte and do not require robust, rigid packaging for containment. Consequently they can be thinner, lighter and more flexible. However, solid-state supercapacitors suffer from lower power density and where new materials have been developed to improve performance, there remains a gap between promising laboratory results that usually require nano-structured materials and fine-scale processing approaches and current manufacturing technology that operates at large scale. We demonstrate a new, scalable capability to produce discrete, multi-layered electrodes with a different material and/or morphology in each layer and where each layer plays a different, critical role in enhancing the dynamics of charge/discharge. This layered structure allows efficient utilisation of each material and enables conservative use of hard-to-obtain materials. The layered electrode shows amongst the highest combinations of energy and power densities for solid-state supercapacitors. Our functional design and spray manufacturing approach to heterogeneous electrodes provide a new way forward for improved energy storage devices.

Aqueous suspensions of multi-wall carbon nanotubes (MWNTs) in dilute H₂SO₄ were sprayed onto both sides of a Nafion membrane and dried to fabricate flexible solid-state supercapacitors. A single cell with MWNT-only electrodes had a capacitance of 57 F g⁻¹ per electrode at 2 mV s⁻¹ and 44 F g⁻¹ at 150 mV s⁻¹ but with low H⁺ mobility. Cells with MWNT + ionomer hybrid electrodes showed higher H⁺ mobility, and the electric double layer (EDL) capacitance increased to 145 F g⁻¹ at 2 mV s⁻¹ and 91 F g⁻¹ at 150 mV s⁻¹. The energy and power densities of one electrode charged to 1 V at 1 A g⁻¹ were 12.9 Wh kg⁻¹ and 3.3 kW kg⁻¹ respectively. Three solid-state supercapacitor cells connected in series charged to 3 V at 1 and 2 A g⁻¹ provided a device power density of 8.9 kW kg⁻¹ at 1 A g⁻¹ and 9.4 kW kg⁻¹ at 2 A g⁻¹, the highest for all-solid-state EDL supercapacitors.

Si-based high-capacity materials have gained much attention as an alternative to graphite in Li-ion battery anodes. Although Si additions to graphite anodes are now commercialized, the fraction of Si that can be usefully exploited is restricted due to its poor cyclability arising from the large volume changes during charge/discharge. Si/SiO_x nanocomposites have also shown promising behavior, such as better capacity retention than Si alone because the amorphous SiO_x helps to accommodate the volume changes of the Si. Here, we demonstrate a new electrode architecture for further advancing the performance of Si/SiO_x nanocomposite anodes using a scalable layer-by-layer atomization spray deposition technique. We show that particulate C interlayers between the current collector and the Si/SiO_x layer and between the separator and the Si/SiO_x layer improved electrical contact and reduced irreversible pulverization of the Si/SiO_x significantly. Overall, the multiscale approach based on microstructuring at the electrode level combined with nanoengineering at the material level improved the capacity, rate capability, and cycling stability compared to that of an anode comprising a random mixture of the same materials.

A one-step scalable spray technique was used to fabricate solid-state supercapacitors with multi-wall carbon nanotube/TiO₂-nanoparticle/ionomer hybrid electrodes. The 3D electrode nanostructure was designed for mobile H⁺ ion generation and fast electron-ion dual conduction, achieving an unusual and highly attractive balance of energy (31.8 W h kg⁻¹) and power (14.9 kW kg⁻¹) densities at 1 A g⁻¹ that are amongst highest reported for solid-state supercapacitors.