Improvement in Cycle Life of Organic Lithium-Ion Batteries by In-Cell Polymerization of Tetrathiafulvalene-Based Electrode Materials

Abstract

Redox-active organic molecules are promising candidates for next-generation electrode materials. Nevertheless, finding low-molecular-weight organic materials with a long cycle life remains a crucial challenge. Herein, we demonstrate the application of tetrathiafulvalene and its vinyl analogue bearing triphenylamines as long-cycle-life electrodes for lithium-ion batteries (LIBs). These molecules were successfully synthesized using palladium-catalyzed C–H arylation. Electrochemical analysis revealed that a polymer formed on the electrode. LIBs comprising these molecules exhibited noteworthy charge–discharge properties with a long cycle life (the capacity after 100 cycles was greater than 90% of the discharge capacity in the third cycle) and a high utilization ratio (approximately 100%). “In-cell” polymerization during the first charge process is considered to contribute to the effect. This study indicates new avenues for the creation of organic materials for rechargeable batteries.

Electron Storage Performance of Metal–Organic Frameworks Based on Tetrathiafulvalene–Tetrabenzoate as Cathode Active Materials in Lithium- and Sodium-Ion Batteries

“…The first organometallic TTF-TCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane) charge-transfer salt was reported in 1973, leading to numerous reports on other synthetic conductors . Recently, TTF has been incorporated into several molecular and supramolecular systems, which are widely applied in various fields such as conductive, , magnetic, − catalytic, , and optoelectronic materials. , Because TTF derivative donors show reversible and stable 2-electron redox reactions at high potentials, as shown in Figure , − they have been applied as cathode materials in rechargeable batteries. − …”

Synthesis of Bz-TTFs with polymerization sites and the properties of Li-ion batteries comprising them as active materials

“…These results were similar to those of TTF-4TPA. 19 The rate performance of the in-cell polymerized 1 /Li was investigated at different current densities of 0.1–20 A g −1 and in a voltage range of 2.5–4.3 V after 10 cycles. The electrode containing 50 wt% of 1 also showed similar performances, exhibiting approximately 51% of the capacity of the electrodes containing 10 wt% of 1 (Fig.…”

“…S7b, ESI†). 19,27 The charge–discharge parameters for the rechargeable batteries using 1 and 2 are summarized in Table S2 (ESI†). The average voltages for the first discharge cycle for 1 and 2 were 3.37 V ( vs. Li/Li + ) and 3.24 V for 2 , respectively, and the energy densities for the first discharge cycle for 1 and 2 were 445 mW h g −1 and 411 mW h g −1 , respectively.…”

“…Our group has previously proposed the redox and polymerization processes for TTF-4TPA to rationalize in-cell polymerization. 19 Because of the high resemblance between the properties of 1 and TTF-4TPA, it was speculated that the redox and polymerization processes of 1 proceeded according to Scheme S1 (ESI†), where neutral 1 might repeat the redox and polymerization reactions to form the tetracation of polymer- 1 via eight-electron redox reactions. After generating the tetracation of polymer- 1 , it may be changed to the neutral form of polymer- 1 , via a four-electron redox reduction reaction.…”

“…1) as long-cycle-life electrodes for LIBs via the ''in-cell polymerization'' technique. 19 The most important point of the design was that polymers could be generated without redox-inactive linkages since the TPA moieties could couple during the charging process with each other at the paraposition carbon on the benzene rings. TTF-4TPA undergoes a fourteen-electron oxidation reaction during the initial charge process.…”