N‐Containing Carbon‐Coated β‐Si3N4 Enhances Si Anodes for High‐Performance Li‐Ion Batteries

Abstract

Abstract The lithiation/delithiation properties of α‐Si3N4 and β‐Si3N4 are compared and the carbon coating effects are examined. Then, β‐Si3N4 at various fractions is used as the secondary phase in a Si anode to modify the electrode properties. The incorporated β‐Si3N4 decreases the crystal size of Si and introduces a new NSiO species at the β‐Si3N4/Si interface. The nitrogen from the milled β‐Si3N4 diffuses into the surface carbon coating during the carbonization heat treatment, forming pyrrolic nitrogen and CNO species. The synergistic effects of combining β‐Si3N4 and Si phases on the specific capacity are confirmed. The operando X‐ray diffraction and X‐ray photoelectron spectroscopy data indicate that β‐Si3N4 is partially consumed during lithiation to form a favorable Li3N species at the electrode. However, the crystalline structure of the hexagonal β‐Si3N4 is preserved after prolonged cycling, which prevents electrode agglomeration and performance deterioration. The carbon‐coated β‐Si3N4/Si composite anode shows specific capacities of 1068 and 480 mAh g−1 at 0.2 and 5 A g−1, respectively. A full cell consisting of the carbon‐coated β‐Si3N4/Si anode and a LiNi0.8Co0.1Mn0.1O2 cathode is constructed and its properties are evaluated. The potential of the proposed composite anodes for Li‐ion battery applications is demonstrated.

Keywords

• beta silicon nitride fraction
• carbon coating
• lithium nitride
• operando X‐ray diffraction
• silicon nitride allotrope