Quantitatively Regulated Adsorption Behavior of Black Liquor‐Derived Carbon Anode for High‐Performance Potassium‐Ion Batteries

Carbonaceous anode showcases great potential for potassium-ion batteries, yet their performance is unsatisfactory. Doping nitrogen atoms and increasing the specific surface area are two popular strategies for boosting the adsorption behavior, resulting in fast reaction kinetics, increased capacity, and long durability. However, rationally regulating the nitrogen content and specific surface area remains challenging, and their effect on adsorption behavior lacks quantified investigations. Here, we synthesize black liquor-derived carbon anodes, where nitrogen content and specific surface area are precisely controlled through a chemical grafting strategy combined with varying pyrolysis temperatures. A concept of average adsorption sites is proposed for evaluating the adsorption behavior. For the first time, it is revealed that the adsorption ratio is linear and quantitatively regulated by average adsorption sites. Moreover, an ultrahigh adsorption contribution, low adsorption energy, and superior electrolyte wettability contribute to exceptional electrochemical performance. As a result, the anode achieved high capacities of 389.2 mAh g^-1 after 200 cycles at 100 mA g^-1, 288.2 mAh g^-1 after 2500 cycles at 1000 mA g^-1, and 183.7 mAh g^-1 after 5000 cycles at 2000 mA g^-1. This study paves the way for rationally regulating the adsorption behavior of carbonous anode materials for potassium-ion batteries.