[en] An electrochemical cell has been constructed for in situ neutron diffraction studies of lithium-insertion/extraction processes in electrode materials for Li-ion batteries. Its key components are a Pyrex tube, gold plated on its inside, which functions as a current collector, and a central lithium rod, which serves as the negative electrode. The device is demonstrated here for a neutron diffraction study of lithium extraction from LiMn₂O₄: a mechanical Celgard separator soaked in the electrolyte surrounds the lithium electrode. The LiMn₂O₄ powder, mixed with electrolyte, occupies the space between separator and current collector. (orig.)