Silicon is a promising material for anodes in energy-storage devices. However, excessive growth of a solid-electrolyte interphase (SEI) caused by the severe volume change during the (de)lithiation processes leads to dramatic capacity fading. Here, we report a super-concentrated electrolyte composed of lithium bis(fluorosulfonyl)imide (LiFSI) and propylene carbonate (PC) with a molar ratio of 1:2 to improve the cycling performance of silicon nanoparticles (SiNPs). The SiNP electrode shows a remarkably improved cycling performance with an initial delithiation capacity of approximately 3000 mAh g and a capacity of approximately 2000 mAh g after 100 cycles, exhibiting about 6.8 times higher capacity than the cells with dilute electrolyte LiFSI-(PC) . Raman spectra reveal that most of the PC solvent and FSI anions are complexed by Li to form a specific solution structure like a fluid polymeric network. The reduction of FSI anions starts to play an important role owing to the increased concentration of contact ion pairs (CIPs) or aggregates (AGGs), which contribute to the formation of a more mechanically robust and chemically stable complex SEI layer. The complex SEI layer can effectively suppress the morphology evolution of silicon particles and self-limit the excessive growth, which mitigates the crack propagation of the silicon electrode and the deterioration of the kinetics. This study will provide a new direction for screening cycling-stable electrolytes for silicon-based electrodes.

Nickel-rich layered oxides, as the most promising commercial cathode material for high-energy density lithium-ion batteries, experience significant surface structural instabilities that lead to severe capacity deterioration and poor thermal stability. To address these issues, radially aligned grains and surface Li x Ni y W z O-like heterostructures are designed and obtained with a simple tungsten modification strategy in the LiNi0.91Co0.045Mn0.045O2 cathode. The formation of radially aligned grains, manipulated by the WO3 modifier during synthesis, provides a fast Li+ diffusion channel during the charge/discharge process. Moreover, the tungsten tends to enter into the lattice of the primary particle surface, and the armor-type tungsten-rich heterostructure protects the bulk material from microcracks, structural transformations, and surface side reactions. First-principles calculations indicate that oxygen is more stable in the surface tungsten-rich heterostructure than elsewhere, thus triggering an improved surface structural stability. Consequently, the 2 wt % WO3-modified LiNi0.91Co0.045Mn0.045O2 (NCM@2W) material shows outstanding prolonged cycling performance (capacity retention of 80.85% after 500 cycles) and excellent rate performance (5 C, 188.4 mA h g–1). In addition, its layered-to-rock salt phase transition temperature is increased by 80 °C compared with that of the pristine cathode. This work provides a novel surface modification approach and an in-depth understanding of the overall performance enhancement of nickel-rich layered cathodes.

As a promising anode material, silicon has attracted extensive attention. The instability of the electrode/electrolyte interphase due to the inherent volume variation upon (de)lithiation is one of the major factors limiting the commercialization of silicon anode materials. Here, we report a concentrated electrolyte with lithium bis(fluorosulfonyl)imide (LiFSI) and lithium difluoro (oxalate) borate (LiDFOB) dual salt to enhance the control of the species constituting the solid electrolyte interphase (SEI) on the surface of the silicon material. The silicon nanoparticle (SiNP) electrode with the dual‐salt LiFSI0.7LiDFOB0.3‐(PC)4 concentrated electrolyte delivers a relatively high average coulombic efficiency of 97.68 % and a remarkably improved cycling performance with an initial capacity of approximately 3300 mAh g−1 and a capacity retention around 2000 mAh g−1 after 100 cycles. It is found that the polarity of the B−F bond of LiDFOB decreases when the molar ratio of LiDFOB to LiFSI is greater than 0.3 : 0.7. Therefore, the reduction of LiDFOB through a ring‐opening reaction coupled with a ring‐opening reaction of PC becomes dominant. The SEI layer rich in the corresponding products Li(BF2O)n polymer could suppress the rupture of the Si particles and excessive growth of the SEI layer, thus could further mitigate the decrease of coulombic efficiency.