All solid-state lithium batteries (ASLBs) are regarded to deliver higher energy density and safety than conventional lithium-ion batteries (LiBs). The higher energy density was because of employing high energy electrodes and unique battery structure designs, like bipolar stacking. In contrast to the conventional LiBs that are sealed separately and then packed together, the solid electrolyte (SE) enables ASLBs to be directly connected without extra packing materials. The bipolar stacking design could minimize the using of inactive material in the batteries resulting a greatly increased energy density. Moreover, if the batteries are connected in series, a high voltage output could be obtained. In addition, the adjacent ASLBs could share one current collector. The shortened electron conduction paths between cells benefit lower resistance and increased power density. Sulfide SEs which are highlighted with ultrahigh ionic conductivity, are one of the most promising electrolytes to produce the bipolar stacked ASLBs. However, the report on sulfide-based ASLBs is rare. The main reason is the lack of reliable laminated electrodes and electrolytes layers.

Herein, based on sulfide SE, we successfully assembled bipolar stacked ASLBs through facilely stacking freestanding cathode, electrolyte, and anode layers. A Li_xSiO₃ coated single crystal NMC 811 was utilized as cathode. A Silicon composite anode was used as anode. Benefiting from the excellent compatibility among sulfide SE, toluene, and ethyl cellulose, a vacuum filtration method is successfully used to prepare freestanding, flexible, and robust cathode, electrolyte, and anode layers. A stainless steel foil was utilized as the current collector for both cathode and anode. As a result, the bipolar stacked ASLBs was successfully fabricated. The doubly stacked cells deliver a high voltage of 8.2 V and cell level energy density of 204 Wh kg^-1 which is much higher than the 189 Wh kg^-1 of ASLBs in conventionally stacked. Our work will pave the way to use sulfide SE to fabricate ASLBs with bipolar stacking designs.