Aqueous PVP-to-HOC Conversion Enables Binder/Current-Collector Free Flexible LMO Cathodes with High Energy

Abstract

Aqueous processing that is both binder- and current-collector free, is an attractive route toward practical flexible cathodes. However, maintaining intimate and durable contact between micron-scale LiMn2O4 (LMO) particles and carbon scaffolds remains challenging at low processing temperatures. Here we use poly(vinylpyrrolidone) (PVP) as a dual-role additive that (i) disperses CNTs and µm-scale LMO uniformly in water and (ii) converts in situ at 300 °C (inert) into a conformal hybrid-organic carbon (HOC) interlayer that “glues” particles to the sp2 network. Temperature screening (200-450 ºC) identifies ~300 ºC as an effective low-T window compatible with free-standing flexibility and LMO stability. In half-cells, the HOC-enabled film (HOC-CNT/LMO) delivers 121.0/120.8 mAh g⁻¹ with 99.9% CE at the 100th cycle, outperforming a PVP-only control (P-CNT/LMO, 99.8/98.6 mAh g⁻¹, 99.9% CE). The device attains full cell-level specific energy of 195 Wh kg⁻¹ at the 100th cycle, approximately twice that of the singly modified full cell and over an order of magnitude higher than the conventional LMO/Al@LTO/Cu configuration. Density-functional theory links the interfacial gains to a smaller gap for the graphene-HOC interface (2.54 eV vs 3.56 eV), π-delocalized frontier orbitals, and broader non-covalent dispersion, consistent with stronger electronic coupling to CNTs. Collectively, the PVP￫HOC route provides an all-aqueous, low-temperature strategy to engineer conformal interlayers that stabilize LMO interfaces and enable robust, flexible, high-performance CNT/LMO cathodes without NMP, polymer binder, or metal current collector.