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.

Metal-organic frameworks (MOFs) exhibit a crystalline structure composed of well-dispersed metal centers separated by organic linker molecules. The aim of this work is to understand and utilize the redox-activity of the metal ion nodes and organic linker molecules in order to employ MOFs in the field of battery applications. In this study, a copper-based MOF has been synthesized with a radical anionic linker using 7,7,8,8-tetracyanoquinodimethane (TCNQ). The Cu(TCNQ) MOF shows a reversible reaction with PF 6 − anions of the electrolyte when applied as positive electrode material in a lithium metal cell. Cyclic voltammetry and constant current cycling studies reveal a different capacity retention behavior depending on the potential range of charge/discharge cycles. In situ X-ray diffraction and ex situ X-ray photoelectron spectroscopy measurements indicate that Cu(TCNQ) undergoes a conversion reaction with the PF 6 − anions going along with the formation of a new crystalline phase at a potential of 3.75 V vs. Li/Li + . The observed reversible storage of anions might open a new door for the application of MOFs as anion host material for dual-ion batteries. As a result of this work, for dual-ion batteries, two classes of cathode materials have to be regarded in the future, "conversion" and "insertion" materials.

Dual‐graphite batteries (DGBs), being an all‐graphite‐electrode variation of dual‐ion batteries (DIBs), have attracted great attention in recent years as a possible low‐cost technology for stationary energy storage due to the utilization of inexpensive graphite as a positive electrode (cathode) material. However, DGBs suffer from a low specific energy limited by the capacity of both electrode materials. In this work, a composite of black phosphorus with carbon (BP‐C) is introduced as negative electrode (anode) material for DIB full‐cells for the first time. The electrochemical behavior of the graphite || BP‐C DIB cells is then discussed in the context of DGBs and DIBs using alloying anodes. Mechanistic studies confirm the staging behavior for anion storage in the graphite positive electrode and the formation of lithiated phosphorus alloys in the negative electrode. BP‐C containing full‐cells demonstrate promising electrochemical performance with specific energies of up to 319 Wh kg–1 (related to masses of both electrode active materials) or 155 Wh kg–1 (related to masses of electrode active materials and active salt), and high Coulombic efficiency. This work provides highly relevant insights for the development of advanced high‐energy and safe DIBs incorporating BP‐C and other high‐capacity alloying materials in their anodes.

MXenes have emerged as one of the most interesting material classes, owing to their outstanding physical and chemical properties enabling the application in vastly different fields such as electrochemical energy storage (EES). MXenes are commonly synthesized by the use of their parent phase, i.e., MAX phases, where “M” corresponds to a transition metal, “A” to a group IV element, and “X” to carbon and/or nitrogen. As MXenes display characteristic pseudocapacitive behaviors in EES technologies, their use as a high-power material can be useful for many battery-like applications. Here, a comprehensive study on the synthesis and characterization of morphologically different titanium-based MXenes, i.e., Ti3C2 and Ti2C, and their use for lithium-ion batteries is presented. First, the successful synthesis of large batches (≈1 kg) of the MAX phases Ti3AlC2 and Ti2AlC is shown, and the underlying materials are characterized mainly by focusing on their structural properties and phase purity. Second, multi- and few-layered MXenes are successfully synthesized and characterized, especially toward their ever-present surface groups, influencing the electrochemical behavior to a large extent. Especially multi- and few-layered Ti3C2 are achieved, exhibiting almost no oxidation and similar content of surface groups. These attributes enable the precise comparison of the electrochemical behavior between morphologically different MXenes. Since the preparation method for few-layered MXenes is adapted to process both active materials in a “classical” electrode paste processing method, a better comparison between both materials is possible by avoiding macroscopic differences. Therefore, in a final step, the aforementioned electrochemical performance is evaluated to decipher the impact of the morphology difference of the titanium-based MXenes. Most importantly, the delamination leads to an increased non-diffusion-limited contribution to the overall pseudocapacity by enhancing the electrolyte access to the redox-active sites.

Faradaic reactions including charge transfer are often accompanied with diffusion limitation inside the bulk. Conductive two-dimensional frameworks (2D MOFs) with a fast ion transport can combine bothcharge transfer and fast diffusion inside their porous structure. To study remaining diffusion limitations caused by particle morphology, different synthesis routes of Cu-2,3,6,7,10,11-hexahydroxytriphenylene (Cu 3 (HHTP) 2 ), a copper-based 2D MOF, are used to obtain flake-and rod-like MOF particles. Both morphologies are systematically characterized and evaluated for redox-active Li + ion storage. The redox mechanism is investigated by means of X-ray absorption spectroscopy, FTIR spectroscopy and in situ XRD. Both types are compared regarding kinetic properties for Li + ion storage via cyclic voltammetry and impedance spectroscopy. A significant influence of particle morphology for 2D MOFs on kinetic aspects of electrochemical Li + ion storage can be observed. This study opens the path for optimization of redox active porous structures to overcome diffusion limitations of Faradaic processes.

Carbons are considered as anode active materials in potassiumion batteries (PIBs). Here, the correlation between material properties of disordered (non-graphitic) and ordered graphitic carbons and their electrochemical performance in carbon j j K metal cells is evaluated. First, carbons obtained from heat treatment of petroleum coke at temperatures from 800 to 2800 °C are analyzed regarding their microstructure and surface properties. Electrochemical performance metrics for K + ion storage like specific capacity and Coulombic efficiency (C Eff ) are correlated with surface area, non-basal planes and microstructure properties, and compared to Li + ion storage. For disordered carbons, the specific capacity can be clearly correlated with the defect surface area. For highly ordered graphitic carbons, the degree of graphitization strongly determines the specific capacity. The initial C Eff of graphitic carbons shows a strong correlation with basal and non-basal planes. Second, kinetic limitations of ordered graphitic carbons are reevaluated by analyzing commercial graphites regarding particle size and surface properties. A clear correlation between particle size, surface area and well-known challenges of graphitic carbons in terms of low-rate capability and voltage hysteresis is observed. This work emphasizes the importance of bulk and surface material properties for K + ion storage and gives important insights for future particle design of promising carbon anodes for PIB cells.