To address these limitations, approaches that use composite electrode materials are being pursued. On the one hand, there is the simple mixing of active material with conductive additives such as carbon black, nanotubes or graphene. More sophisticated structures have been developed (Fig. 4a–d), where one material serves as a conductive backbone for the electrochemically active material, thus providing structural integrity and mechanical stability, in addition to enhancing the electronic conductivity of the electrode. Ideally, well-designed composite electrodes should provide synergistic benefits in terms of electrochemical and mechanical properties. The latter are especially important for current collector-free and wearable devices50. Poor mechanical strength also leads to faster electrode (and device) degradation1.