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Three-dimensional porous composite microspheres of LiFePO4 and nitrogen-doped graphene have been synthesized by a solvothermal process coupled with subsequent calcination.

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The cyclic stability of Si anodes is still a great challenge for high-performance lithium-ion batteries due to the huge volume change. In this work, the continuous volume expansion of the Si anode and individual nanoparticles during cycling is deeply investigated by various visualization observations, and it is effectively suppressed by an artificial solid electrolyte interphase (SEI) consisting of inner polydopamine and outer natural SEI. Visualization characterization unveils the mechanism of action of the artificial SEI in Si nanoparticles. Specifically, repeated plastic deformation causes the transformation from amorphous Si into clusters accompanied by interstitial space, which induces continuous volume expansion, and the high-modulus artificial SEI accommodates plastic deformation of Si clusters during cycling, holding the structural integrity of Si nanoparticles. The anode of Si nanoparticles anchored on expanded graphite with such artificial SEI achieves its theoretical specific capacity and maintains a discharge capacity close to 80% of the maximum (983 mAh g–1), with little fading after 500 cycles. This work not only expands upon the understanding of plastic deformation and SEI but also provides some valuable information for the rational design of Si-based active materials.

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