Boosting the cell performance of the SiO_x@C anode material via rational design of a Si‐valence gradient

Abstract Relieving the stress or strain associated with volume change is highly desirable for high‐performance SiO_x anodes in terms of stable solid electrolyte interphase (SEI)‐film growth. Herein, a Si‐valence gradient is optimized in SiO_x composites to circumvent the large volume strain accompanied by lithium insertion/extraction. SiO_x@C annealed at 850°C has a gentle Si‐valence gradient along the radial direction and excellent electrochemical performances, delivering a high capacity of 506.9 mAh g⁻¹ at 1.0 A g⁻¹ with a high Coulombic efficiency of ~99.8% over 400 cycles. Combined with the theoretical prediction, the obtained results indicate that the gentle Si‐valence gradient in SiO_x@C is useful for suppressing plastic deformation and maintaining the inner connection integrity within the SiO_x@C particle. Moreover, a gentle Si‐valence gradient is expected to form a stress gradient and affect the distribution of dangling bonds, resulting in local stress relief during the lithiation/delithiation process and enhanced Li‐ion kinetic diffusion. Furthermore, the lowest interfacial stress variation ensures a stable SEI film at the interface and consequently increases cycling stability. Therefore, rational design of a Si‐valence gradient in SiO_x can provide further insights into achieving high‐performance SiO_x anodes with large‐scale production.