# Manipulating Interphase Chemistry by Endogenous Doping Toward High-Performance Hard Carbon Anodes for Sodium-Ion Batteries

## TL;DR

This paper introduces a new method to improve hard carbon anodes in sodium-ion batteries by using endogenous doping to create a better interphase layer, leading to better performance and stability.

## Contribution

The novel contribution is using endogenous N/S doping via the Maillard reaction to manipulate interphase chemistry for enhanced battery performance.

## Key findings

- Endogenous doping creates an inorganic-enriched SEI layer, improving rate, ICE, and cycling performance.
- The full cell with Na3V2(PO4)3 cathode shows 89.2% capacity retention over 700 cycles at 1 C.
- Pouch cells with high cathode mass loading maintain 98.1% capacity retention after 175 cycles at 1 C.

## Abstract

Based on the Maillard reaction principle, an endogenous doping strategy was developed to induce the formation of a rich-inorganic solid–electrolyte interphase (SEI) layer on a hard carbon anode.The hard carbon anode with inorganic-enriched SEI layer delivers enhanced rate, high initial coulombic efficiency and stable cycling performance.The assembled full cell with a Na3V2(PO4)3 cathode exhibits excellent cycling stability over 700 cycles, achieving a capacity retention of 89.2% at 1 C with an N/P ratio of 1.12.

Based on the Maillard reaction principle, an endogenous doping strategy was developed to induce the formation of a rich-inorganic solid–electrolyte interphase (SEI) layer on a hard carbon anode.

The hard carbon anode with inorganic-enriched SEI layer delivers enhanced rate, high initial coulombic efficiency and stable cycling performance.

The assembled full cell with a Na3V2(PO4)3 cathode exhibits excellent cycling stability over 700 cycles, achieving a capacity retention of 89.2% at 1 C with an N/P ratio of 1.12.

The online version contains supplementary material available at 10.1007/s40820-026-02124-9.

The practical of hard carbon (HC) anodes in sodium-ion batteries is primarily limited by their unsatisfactory initial coulombic efficiency (ICE), cycling stability and rate performance, which are closely related to their interphase chemistry and microstructure. Herein, a unique manipulating interphase chemistry strategy by endogenous N/S doping is proposed to simultaneously achieve the both issues. Specifically, a series of reducing sugars and amino acid have been proven to trigger the Maillard reaction, thereby enabling endogenous N/S doping and microstructural design for HC anodes. Endogenous doping facilitates the formation of an inorganic-enriched solid–electrolyte interface (SEI) layer on cycled HC, which can effectively accelerate ion transport kinetics and reduce side effects for enhanced rate, ICE, cycling performance and reversible capacity. Meanwhile, the increase in the number of closed pores boosts both the platform capacity and cycling stability of HC. Consequently, the features HC anodes demonstrate a splendid reversible capacity (363 mAh g−1 at 0.05 A g−1), superior cycling performance (over 2500 cycles with 79% retention at 5.0 A g−1) and adequate ICE (89%). The assembled full cell with Na3V2(PO4)3 cathode exhibits splendid cycling stability over 700 cycles with capacity retention of 89.2% at 1 C. Surprisingly, the pouch cell with high cathode mass loading of 20.7 mg cm−1 maintains 98.1% capacity retention after 175 cycles at 1 C. This strategy provides new ideas and insights for the design and screening of high-performance HC anodes.

The online version contains supplementary material available at 10.1007/s40820-026-02124-9.