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Abstract Semiconducting polymers are of interest due to their solution processibility and broad electronic applications. Electrochemistry allows these wide bandgap semiconductors to be converted to conducting polymers by doping such polymers at various potentials. When polymers arep‐doped to improve their conductivity via electrochemical oxidation, various positively‐charged carriers are created, including polarons (singly‐charged) and bipolarons (doubly‐charged). Carrier creation is accompanied by anion intercalation from the electrolyte for charge balance, and this insertion requires ion mobility. In this work, poly(3‐hexylthiophene) (P3HT) with different regioregularities is used to understand the relationship between solvent swelling, which affects anion intercalation, and electrochemical doping. Cyclic voltammetry, optical absorption spectroscopy, and grazing incidence wide‐angle X‐ray scattering (GIWAXS) measurements are used to correlate the doping level with structural changes. In situ electrochemical quartz crystal microbalance (EQCM) measurements are used to quantify the swelling of the polymers dynamically during electrochemical cycling. Lastly, in situ conductivity measurements are done to measure the effect of swelling on the ionic and electronic conductivity. The results indicate that solvent swelling is required for bipolaron formation, and that swelling facilitates both the small structural changes need for polaron formation and the disordering required for bipolaron formation. 

Abstract The growing demand for bioelectronics has generated widespread interest in implantable energy storage. These implantable bioelectronic devices, powered by a complementary battery/capacitor system, have faced difficulty in miniaturization without compromising their functionality. This paper reports on the development of a promising high‐rate cathode material for implantable power sources based on Li‐exchanged Na_1.5VOPO₄F_0.5anchored on reduced graphene oxide (LNVOPF‐rGO). LNVOPF is unique in that it offers dual charge storage mechanisms, which enable it to exhibit mixed battery/capacitor electrochemical behavior. In this work, electrochemical Li‐ion exchange of the LNVOPF structure is characterized by operando X‐ray diffraction. Through designed nanostructuring, the charge storage kinetics of LNVOPF are improved, as reflected in the stored capacity of 107 mAh g⁻¹at 20C. A practical full cell device composed of LNVOPF and T‐Nb₂O₅, which serves as a pseudocapacitive anode, is fabricated to demonstrate not only high energy/power density storage (100 Wh kg⁻¹at 4000 W kg⁻¹) but also reliable pulse capability and biocompatibility, a desirable combination for applications in biostimulating devices. This work underscores the potential of miniaturizing biomedical devices by replacing a conventional battery/capacitor couple with a single power source.