Organic molecules are emerging candidates for the next generation of cost-effective active materials of Li-ion batteries. Small diimide building blocks such as pyromellitic diimide (PMDI) have attracted much attention because of their high theoretical capacity. Many strategies have been undertaken to limit the well-known phenomenon of dissolution of the active material in the electrolyte. Such strategies include the preparation of salts and the synthesis of polyimides or macrocycles. Since dibromopyromellitic dimiide exhibits almost no sp2 cross-coupling polymerization reaction by conventional synthetic routes (Suzuki–Miyaura or Migita–Stille), we used PMDI as an aromatic C–H bond-bearing unit for direct (hetero)­arylation polymerization (DHAP) with 1,4-dibromobenzene as comonomer as a new stabilization strategy. DHAP proved to be an effective tool in the preparation of this polymer, yielding a number-average molecular weight of up to 31 kDa. We studied the effect of side-chain engineering using variable chain lengths, cross-linked structures, and thermocleavable functional groups. Practical potential limits of 1.65 to 2.50 V vs Li/Li+, wherein two distinct redox phenomena appear, and a galvanostatic high rate limit of 2C were determined. Galvanostatic measurements at C/20 show a starting normalized capacity of 0.94 decreasing to 0.48 after more than 80 days (50 cycles). A maximum discharge capacity of 73 mAh/g as a first cycle was obtained for a polymer of this family at C/10. Density functional theory calculations were applied to understand the higher corrected redox potentials obtained by cyclic voltammetry for sodium ion over lithium ion batteries.

A π-conjugated copolymer based on a pyrene diimide unit (P(PyDI-T2)) was synthesized using the Suzuki−Miyaura crosscoupling reaction between 4,5,9,10-pyrene diimide-2,7-diboronic ester and 2,2′-dibromo-5,5′-bithiophene for use as an active material in a Li-ion battery. Usually, diimide molecules are known to demonstrate reversible redox processes with a maximum of a two-electron insertion per unit. The unique structure of pyrene diimide, consisting of a pyrene core bearing two imide functions lying on formal double bonds, was anticipated to potentially demonstrate reversible redox processes involving four electrons per unit via aromatic stabilization. Also, the 2-and 7-positions are much less sterically hindered than similar relative positions in other diimides and hence should permit good electron mobility in the resulting polymer. Unfortunately, we were unable to observe any reduction phenomena in a half-cell (with a Li anode), likely due to negligible electronic conductivity. Subsequently, P(PyDI-T2) was blended with SWCNTs for dispersion in order to enhance both conductivity and surface area. High concentration dispersion was filtered to obtain a freestanding film of P(PyDI-T2)/SWCNT, with an intrinsic conductivity of 30 S/cm, which was used directly as a cathode in the half-cell. Reversible redox pointing to two one-electron phenomena was observed with 40.6 mA h/g at a galvanostatic slow rate of C/50 with a high mass loading of 3.2 mg/cm 2 . Density functional theory calculations were performed on pyrene diimide units to elucidate poor mobility and to compare Gibbs free energies for the second reduction of each site.

New alternating copolymers based on benzo[1,2-b:4,5-b′]-dithiophene and thieno[3,4-d]thiazole derivatives have been synthesized and their optical, electrochemical and photovoltaic properties were studied.