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.

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