Porous Organic Polymer with Hierarchical Structure and Limited Volume Expansion for Ultrafast and Highly Durable Sodium Storage.

Sustainable organic electrode materials, as promising alternatives to conventional inorganic electrode materials for sodium-ion batteries (SIBs), are still challenging to realize long-lifetime and high-rate batteries because of their poor conductivity, limited electroactivity, and severe dissolution. It is also urgent to deeply reveal their electrochemical mechanism and evolution processes. A porous organic polymer (POP) with a conjugated and hierarchical structure is designed and synthesized here. The unique molecule and structure endow the POP with electron delocalization, high ionic diffusivity, plentiful active sites, exceptional structure stability, and limited solubility in electrolytes. When evaluated as an anode for SIBs, the POP exhibits appealing electrochemical properties regarding reversible capacity, rate behaviors, and long-duration life. Importantly, using judiciously combined experiments and theoretical computation, including in situ transmission electron microscopy (TEM), and ex situ spectroscopy, we reveal the Na-storage mechanism and dynamic evolution processes of the POP, including 12-electron reaction process with Na, low volume expansion (125-106% vs the initial 100%), and stable composition and structure evolution during repeating sodiation/de-sodiation processes. This quantitative design for ultrafast and highly durable sodium storage in the POP could be of immediate benefit for the rational design of organic electrode materials with ideal electrochemical properties.