  There is increasing interest in materials that combine energy-storing
functions with augmented mechanical properties, ranging from flexibility in
bending to stretchability to structural properties. In the case of lithium-ion
batteries, these mechanical functions could enable their integration in
emerging technologies such as wearable, free-form electronics and ultimately as
structural elements, for example, in transport applications. This work presents
a method to produce flexible LiFePO4 LFP electrodes with an extraordinary
combination of electrochemical and mechanical performance. Such electrodes
exhibit an exceptionally high specific toughness, combined with superior rate
capability and energy density, with respect to reference electrodes with
typical metallic current collectors. These properties are a result of the
strong adhesion of the active material particles to the high surface area
carbon nanotube fiber fabric, used as a lightweight, tough, and highly
conducting current collector. This strong adherence minimizes electrical
resistance, mitigates interfacial failure, and increases ductility through
heterogeneous strain after cohesive failure of the inorganic phase. As a
result, these electrodes can withstand large deformations before fracture, and,
even after fracture, they retain excellent electrochemical performance,
approximately double that of unstretched, Al-supported LFP electrodes with
equivalent loading.
