Carbon fibre electrodes can enable a solid-state battery to carry mechanical load as normal construction materials. The multifunctionality is promising for most lightweight applications. Like all electrode materials, both volume and elastic moduli of the carbon fibre electrodes change during battery cycling. Such changes jeopardize the mechanical integrity of the battery. This paper contains: - Mechanical experiment on single lithiated carbon fibres is demonstrated. - Volume expansion and elastic moduli change of a carbon fibre electrode are measured. - The transverse modulus of a carbon fibre electrode is doubled after Li insertion.