A battery module comprising: a unit module stack having a structure in which two or more unit modules, each of which comprises two or more battery cells mounted at a cell cover in a state in which the battery cells are electrically connected to each other, and electrode terminal connection parts of which protrude outward from the cell cover in a state in which the electrode terminal connection parts are vertically bent, are stacked; a module case in which the unit modules of the unit module stack are arranged such that the unit modules are connected in series to each other, and electrode terminals (222, 232) of the unit modules are open; a bus bar assembly mounted at the electrode terminals (222, 232) of the unit modules in the module case, the bus bar assembly comprising one or more bus bars for connection in series between the unit modules, the bus bars being mounted in an exposed state; and an electrically insulative cover for covering the bus bar assembly, characterized in that the battery cells are connected in parallel to each other in the unit module, each of the battery cells having a structure in which a positive electrode terminal and a negative electrode terminal are formed at one end of each of the battery cells, and the unit modules are stacked in a state in which the unit modules alternately arranged such that the positive electrode terminal and the negative electrode terminal are adjacent to each other between adjacent ones of the unit modules, and the battery cells of the unit modules are connected in parallel to each other in a state in which the electrode terminals (222, 232) are directly coupled to each other and form the electrode terminal connection parts, and the electrode terminal connection parts are vertically bent such that the electrode terminal connection parts have welding surfaces, with which the bus bars of the bus bar assembly come into contact. a unit module stack having a structure in which two or more unit modules, each of which comprises two or more battery cells mounted at a cell cover in a state in which the battery cells are electrically connected to each other, and electrode terminal connection parts of which protrude outward from the cell cover in a state in which the electrode terminal connection parts are vertically bent, are stacked; a module case in which the unit modules of the unit module stack are arranged such that the unit modules are connected in series to each other, and electrode terminals (222, 232) of the unit modules are open; a bus bar assembly mounted at the electrode terminals (222, 232) of the unit modules in the module case, the bus bar assembly comprising one or more bus bars for connection in series between the unit modules, the bus bars being mounted in an exposed state; and an electrically insulative cover for covering the bus bar assembly, characterized in that the battery cells are connected in parallel to each other in the unit module, each of the battery cells having a structure in which a positive electrode terminal and a negative electrode terminal are formed at one end of each of the battery cells, and the unit modules are stacked in a state in which the unit modules alternately arranged such that the positive electrode terminal and the negative electrode terminal are adjacent to each other between adjacent ones of the unit modules, and the battery cells of the unit modules are connected in parallel to each other in a state in which the electrode terminals (222, 232) are directly coupled to each other and form the electrode terminal connection parts, and the electrode terminal connection parts are vertically bent such that the electrode terminal connection parts have welding surfaces, with which the bus bars of the bus bar assembly come into contact.