Nitrogen-doped Co₃O₄ spheres confined in carbon layers as anodes for enhanced lithium storage

Lithium storage in transition metal oxides (TMOs) shows promise for achieving a substantial reversible capacity due to their capability for multielectron transfer during redox reactions. TMOs suffer from inherent drawbacks, notably limited electronic conductivity, and tendency for side reactions with electrolytes resulting in suboptimal rate capabilities and unsatisfactory cycling performance. This study introduces a novel approach wherein nitrogen-doped cobalt oxide encapsulated within a carbon matrix (N-Co₃O₄@C) is synthesized through a hydrothermal method, with aim of enhancing both the internal and external electronic conductivity. Transmission electron microscopy revealed the successful confinement of Co₃O₄ within a 3–5 nm carbon layer, effectively mitigating particle agglomeration issues observed in uncoated counterparts. Ex-situ X-ray diffraction analyses confirm that N-Co₃O₄@C preserves its original active material during cycling. In contrast, the unmodified material exhibits capacity loss due to its conversion into CoO. Consequently, N-Co₃O₄@C demonstrates a reversible specific capacity of 1310.4 mAh g⁻¹ at 0.1 A g⁻¹ within a potential range of 0.01–3.0 V (vs. Li/Li⁺) along initial Coulombic efficiency of 85.4%. It sustains capacity retention of 97.8% at 0.1 A g⁻¹ over 100 cycles. This strategy introduces a promising methodology for stabilizing TMOs during lithiation and delithiation by boosting both internal and external electronic conductivity.