Unlocking Full Discharge Capacities of Poly(vinylphenothiazine) as Battery Cathode Material by Decreasing Polymer Mobility Through Cross‐Linking

Abstract

Organic cathode materials are a sustainable alternative to transition metal oxide‐based compounds in high voltage rechargeable batteries due to their low toxicity and availability from less‐limited resources. Important criteria in their design are a high specific capacity, cycling stability, and rate capability. Furthermore, the cathode should contain a high mass loading of active material and be compatible with different anode materials, allowing for its use in a variety of cell designs. Here, cross‐linked poly(3‐vinyl‐N‐methylphenothiazine) as cathode‐active material is presented, which shows a remarkable rate capability (up to 10C) and cycling stability at a high and stable potential of 3.55 V versus Li/Li+ and a specific capacity of 112 mAh g−1. Its use in full cells with a high mass loading of 70 wt% is demonstrated against lithium titanate as intercalation material as well as lithium metal, which both show excellent performance. Through comparison with poly(3‐vinyl‐N‐methylphenothiazine) the study shows that changing the structure of the redox‐active polymer through cross‐linking can lead to a change in charge/discharge mechanism and cycling behavior of the composite electrode. Poly(3‐vinyl‐N‐methylphenothiazine) in its cross‐ and non‐cross‐linked form both show excellent results as cathode‐active materials with variable specifications regarding specific capacity, cycling stability, and rate capability.

Phenothiazine‐Functionalized Poly(norbornene)s as High‐Rate Cathode Materials for Organic Batteries

“…To improve the latter, a carbon‐based conductive additive is usually added to the electrode, and solubility can be suppressed by incorporating redox‐active moieties into polymeric architectures . It is important, however, to consider the insolubility of the redox polymer in both its neutral and charged state, and in some cases crosslinking is required . The redox‐active unit determines the charge/discharge potential of the battery.…”

“…Another redox‐active group with a similar oxidation potential is phenothiazine (PT). We, among other groups, have investigated PT‐based polymers as cathode materials. In particular poly(3‐vinyl‐ N ‐methylphenothiazine) (PVMPT) showed excellent results regarding cycling stability and rate capability .…”

“…We, among other groups, have investigated PT‐based polymers as cathode materials. In particular poly(3‐vinyl‐ N ‐methylphenothiazine) (PVMPT) showed excellent results regarding cycling stability and rate capability . For the non‐crosslinked derivative, however, strong π‐interactions led to only half of the theoretical specific capacity being accessible .…”

Recent Progress in Multivalent Metal (Mg, Zn, Ca, and Al) and Metal‐Ion Rechargeable Batteries with Organic Materials as Promising Electrodes

“…To gain insight into these issues, effective approaches are encouraged to be proposed to improve the current situation of organic‐electrode‐based multivalent metal and metal‐ion batteries. Actually, recent successful strategies from organic lithium (Li)‐ion batteries based on conductive polymers, conjugated polymers, carbonyl compounds,[37a,41‐48] and new redox chemistry compounds afford us sufficient experiences that merit attention. Innovative demonstrations including all‐organic‐electrode and all‐solid‐state batteries have also been realized based on these materials .…”

Phosphaviologen‐Based Pyrene‐Carbon Nanotube Composites for Stable Battery Electrodes

“…There is a large body of literature developing organic moieties to use in electrode materials, however, relatively few classes of moieties possess discharge voltages greater than 3.0 V versus Li/Li + . [7,17,19] Currently, nitroxide based radicals, [20][21][22][23] sulfur and nitrogen containing heteroaromatics, [24][25][26][27] and aromatic quinones [19,[28][29][30][31] are promising molecular architectures that exhibit high voltages in Li-ion batteries, but more suitable moieties and functional groups need to be developed to achieve organic batteries having high energy and power densities. Molecular design motifs that allow electroactive organic molecules to better interface with conductive additives would prevent electrode dissolution and increase conductivity, potentially increasing stability and rate performance.…”