Here, we bring to the readers the outcome of Group 1 discussion: Future after lithium. The group has covered battery chemistries that are often being considered as "post-Li" battery technologies. After extensive deliberations, the group concluded that the current vibe about the need of future technologies after the lithium era and, thus, the quest for which new technologies can replace lithium-based battery technology, are somewhat inappropriate and misleading (partially incorrect), respectively. The discussion group reached the conclusion that it would be wise to approach and refer at these technologies as "side-byside" to Li-based batteries. As such, we elaborate here in details on these "side-by-side" promising technologies.Evaluation of the battery concepts depends on several aspects, among which performance is one of the key parameters. Hence, the performance comparison of different cell chemistry is everything, but immediate. As a matter of the fact, the European Commission, e.g., funded the ETIP Batteries Europe (https:// batterieseurope.eu/) as the "one-stop shop" for the batteryrelated R&I ecosystem and aims to accelerate the establishment of a competitive, sustainable and efficient value chain and globally competitive European battery industry through Research and Innovation. Within this ETIP, several working groups have been established, including the one dealing with new and emerging cell technologies. This group, led by Prof. Edström, Dr. Steven and one of the co-authors of this manuscript (SP), is expected to identify the key performance indicators (KPIs) enabling a fair comparison of commercial, new and emerging cell technologies with respect to their applications. However, these KPIs have not been identified yet. Hence, the current study aims to provide insights into "side-by-side" new emerging technologies and also to report a comparative analysis to Li-ion batteries by using a simple approach (i.e., mainly considering cost, energy density, and cycle life). Nonetheless, due to the fact that most of the "side-by-side" technologies are at the early stage of development, a comparison among them is not trivial. Thus, we point out in this progress report only the possibly suitable applications of the new technologies without a comparison. Sodium-Ion Batteries (Na-Ion) IntroductionTo relieve the environmental issues, solving the problem caused by intermittent availability of renewable energy resource, e.g., solar energy, wind energy and geothermal energy, is mandatory. Thus, energy storage systems, especially electrochemical energy storage (EES) systems including batteries, supercapacitors, etc., are in the focus of intensive research and development efforts. [1][2][3] In 1991, the Japanese Sony Corp. developed the first commercial lithium-ion batteries with LiCoO 2 and graphite as electrode materials. [4,5] With the blooming of portable electronic Yasin Emre Durmus is currently a PostDoc researcher at the Forschungszentrum Jülich (Germany) within the Institute of Fundamental Electrochemistry (IEK-9). ...

Organic redox polymers are attractive electrode materials for more sustainable rechargeable batteries. To obtain full‐organic cells with high operating voltages, redox polymers with low potentials (<2 V versus Li|Li+) are required for the negative electrode. Dibenzo[a,e]cyclooctatetraene (DBCOT) is a promising redox‐active group in this respect, since it can be reversibly reduced in a two‐electron process at potentials below 1 V versus Li|Li+. Upon reduction, its conformation changes from tub‐shaped to planar, rendering DBCOT‐based polymers also of interest to molecular actuators. Here, the syntheses of three aliphatic DBCOT‐polymers and their electrochemical properties are presented. For this, a viable three‐step synthetic route to 2‐bromo‐functionalized DBCOT as polymer precursor is developed. Cyclic voltammetry (CV) measurements in solution and of thin films of the DBCOT‐polymers demonstrate their potential as battery electrode materials. Half‐cell measurements in batteries show pseudo capacitive behavior with Faradaic contributions, which demonstrate that electrode composition and fabrication will play an important role in the future to release the full redox activity of the DBCOT polymers.

Organic electrode materials are considered to be promising candidates for alternative and greener energy storage solutions. Due to their intrinsic low conductivity, however, usually large amounts of conductive additives are required for electrode fabrication. Herein, we investigate electrodes with a 90 wt % active material ratio and high mass loadings of up to 4.3 mg cm–2, which show good cycling performance because of the conjugated copolymer structure chosen for the phenothiazine-based active material. By furthermore reducing the inactive weight within the polymer through structural modification and raising the potential range during constant current measurements we increased the discharge capacity for the whole composite by a factor of 12 to 0.169 mAh cm–2 compared to a previous study. This study demonstrates that conjugated organic copolymers are attractive electrode materials due to their intrinsic conductivity combined with the presence of defined redox centers.

Organic redox polymers are considered a “greener” alternative as battery electrode materials compared to transition metal oxides. Among these, phenothiazine-based polymers have attracted significant attention due to their high redox potential of 3.5 V vs Li/Li+ and reversible electrochemistry. In addition, phenothiazine units can exhibit mutual π-interactions, which stabilize their oxidized states. In poly­(3-vinyl-N-methylphenothiazine) (PVMPT), such π-interactions led to a unique charge/discharge mechanism, involving the dissolution and redeposition of the polymer during cycling, and resulted in an ultrahigh cycling stability. Herein, we investigate these π-interactions in more detail and what effect their suppression by molecular design has on battery performance. Our study includes a dimeric reference compound for PVMPT, polymers with bulky tolyl or mesityl substituents on the phenothiazine units to inhibit π-interactions and alternating copolymers with maleimide groups to increase spatial distancing between phenothiazine groups. UV/vis- and electron paramagnetic resonance (EPR)-spectroscopic as well as electrochemical measurements in composite electrodes demonstrate how the unique structure of PVMPT is instrumental in obtaining a high cycling stability in poly­(vinylene) derivatives of phenothiazine.

Organic redox polymers have received increasing attention as battery electrode materials due to their low toxicity and the possibility to produce them from renewable resources or petroleum. Phenothiazine is a redox-active group with highly reversible redox chemistry. Polymers based on phenothiazine have shown impressive performance as battery cathode materials regarding cycling stability and rate performance. In this chapter, the progress in this field is summarized, specific properties of phenothiazine-based polymers as cathode-active materials are highlighted and future challenges identified.

Organic electrode materials are capable candidates for nextgeneration greener energy storage solutions. One advantage is that their electrochemical performance can be tuned by structural modification. We herein investigate anisyl-substituted poly(vinyl-) and poly(styrylphenothiazines) as positive electrode materials for dual-ion batteries. π-Interactions -characteristic to phenothiazine redox polymers -are facilitated in the poly(styrene) derivatives PSAPT and PSAPT-X-DVB due to the longer spacing between phenothiazine units and polymer backbone and lead to high cycling stabilities, but reduce their specific capacities. In the poly(vinylenes), the linear PVAPT shows high cycling stability but a dissolution/redeposition mechanism, diminishing its capacity, while the cross-linked X-PVAPT demonstrates high cycling stabilities at specific capacities up to 81 mAh g À 1 paired with an excellent rate performance, where 10,000 cycles at 100 C rate proceed with 86 % capacity retention.