performance in high-voltage LIB cells. Our results point out the importance to thoroughly evaluate the impact of the separator on cell performance, especially when it comes to comparison of electrochemical data within the scientific community. Results and Discussion2.1. Impact of PP Membrane and PP Fiber Separators with Different Thicknesses on the "Rollover" Failure

In this study, a new dual‐ion battery (DIB) concept based on an aqueous/non‐aqueous electrolyte is reported, combining high safety in the form of a nonflammable water‐in‐salt electrolyte, a high cathodic stability by forming a protective interphase on the negative electrode (non‐aqueous solvent), and improved sustainability by using a graphite‐based positive electrode material. Far beyond the anodic stability limit of water, the formation of a stage‐2 acceptor‐type graphite intercalation compound (GIC) of bis(trifluoromethanesulfonyl) imide (TFSI) anions from an aqueous‐based electrolyte is achieved for the first time, as confirmed by ex‐situ X‐ray diffraction. The choice of negative electrode material shows a huge impact on the performance of the DIB cell chemistry, i.e., discharge capacities up to 40 mAh g−1 are achieved even at a high specific current of 200 mA g−1. In particular, lithium titanium phosphate (LiTi2(PO4)3; LTP) and lithium titanium oxide (Li4Ti5O12; LTO) are evaluated as negative electrodes, exhibiting specific advantages for this DIB setup. In this work, a new DIB storage concept combining an environmentally friendly, transition‐metal‐free, abundant graphite positive electrode material, and a nonflammable water‐based electrolyte is established, thus paving the path toward a sustainable and safe alternative energy storage technology.

in storage batteries should be low acquisition and minimum maintenance cost, while a high energy density is not of major importance. [7] As sustainable solutions, these systems cannot afford the usage of rare elements (e.g., cobalt and nickel), which directly results in high material cost, and must exhibit extremely long cycle and calendar life. Lithium-ion batteries (LIBs) currently lead the market of high-energy and high-power batteries for portable electronics and transportation purposes. [4,5] Nevertheless, LIBs face the challenges of high cost, material abundance, and sustainability for the stationary market. [8] In recent years, several emerging battery technologies have attracted considerable attention for large-scale stationary energy storage, e.g., sodium-ion [9] and potassium-ion batteries; [10] systems that are key to transforming the energy infrastructure to overcome the intermittency of renewable energy. Among different aforementioned battery technologies, dualion batteries (DIBs) can be very competitive in terms of cost, material abundance, and sustainability for large-scale stationary storage because both the positive (cathode) and negative Safety and cost are the key metrics for large-scale energy storage. Due to the use of nonaqueous electrolytes and transition metal oxides in current lithium-ion battery technologies, safety, cost, and environmental issues are a significant cause for concern. Graphite is a promising cathode material for dual-ion batteries due to its high operating potential, low cost, and high safety. Nevertheless, it is challenging to find a suitable aqueous electrolyte due to the narrow electrochemical stability window (1.23 V). This work presents a graphite || zinc metal aqueous dual-ion battery of ≈2.3-2.5 V, a remarkably high voltage in aqueous zinc batteries, achieving >80% capacity retention after 200 cycles and delivering ≈110 mAh g-1 at a charge/discharge current of 200 mA g-1. A capacity of nearly 60 mAh g-1 is achieved at a charge/ discharge current of 5000 mA g-1. Natural graphite is enabled as a reversible cathode using a highly concentrated lithium-free bisalt aqueous electrolyte.