Battery cell and battery module including the same

A battery cell includes a casing provided with an accommodation space; and an electrode assembly accommodated in the accommodation space and contacting the casing. The electrode assembly may include a negative electrode including a first current collector and a negative electrode mixture applied to the first current collector; a positive electrode including a second current collector and a positive electrode mixture applied to the second current collector; a separator interposed between the positive electrode and the negative electrode; and a guide member accommodating at least one of the negative electrode and the positive electrode and pressurized or stretched by at least one of the negative electrode and the positive electrode to contract or expand.