As one of the most promising alternatives to graphite negative electrodes, silicon oxide (SiO_x) has been hindered by its fast capacity fading. Solid electrolyte interphase (SEI) aging on silicon SiO_x has been recognized as the most critical yet least understood facet. Herein, leveraging 3D focused ion beam-scanning electron microscopy (FIB-SEM) tomographic imaging, we reveal an exceptionally characteristic SEI microstructure with an incompact inner region and a dense outer region, which overturns the prevailing belief that SEIs are homogeneous structure and reveals the SEI evolution process. Through combining nanoprobe and electron energy loss spectroscopy (EELS), it is also discovered that the electronic conductivity of thick SEI relies on the percolation network within composed of conductive agents (e.g., carbon black particles), which are embedded into the SEI upon its growth. Therefore, the free growth of SEI will gradually attenuate this electron percolation network, thereby causing capacity decay of SiO_x. Based on these findings, a proof-of-concept strategy is adopted to mechanically restrict the SEI growth via applying a confining layer on top of the electrode. Through shedding light on the fundamental understanding of SEI aging for SiO_x anodes, this work could potentially inspire viable improving strategies in the future.

Currently, LiFePO₄ is one of the most successfully commercialized cathode materials in the rechargeable lithium-ion battery (LIB) system, owing to its excellent safety performance and remarkable electrochemical properties and is expected to have a broader market in the near future. Although it is widely recognized that the crystalline structure of a cathode material largely dictates its electrochemical properties (e.g. capacity, cycle life and rate capabilities), this intrinsic connection in LiFePO₄ has not been systematically reviewed. Different from the previous reviews, which mainly focus on the improvement of electrochemical performance by all kinds of techniques, in this review, the relationship between its electrochemical performance and bulk/surface structure is reviewed and discussed. First, it is revealed that the intra-particle Li⁺ transfer is influenced by several properties of the bulk, including crystalline structures, antisite defects and electronic structures. Next, it is demonstrated that the surface/interfacial structures of LiFePO₄, which can be reconstructed artificially or spontaneously, also have great impacts on the performances. Lastly, the intrinsic connection between the structure and performance is preliminarily established, showing brand-new perspectives on the strategy for further improvement and contributing to a comprehensive understanding of LiFePO₄.

The impact of surface structure and interface reconstruction on the electrochemical performances of lithium-ion battery cathode materials is summarized.