Li-ion batteries (LIBs) have become the pivotal nexus for energy storage in the modern society. With the rapid development of electric vehicles (EVs), the fast growth of grid-scale energy storage, and a surge of novel applications, batteries with higher specific energies are urgently demanded. Unfortunately, the state-of-the-art LIBs offer energy densities below 250 Wh kg^-1, unable to support application scenarios like ultralong-range EVs, drones, or flying cars, which require batteries with a specific energy of above 350 Wh kg^-1. Silicon anodes or lithium-metal anodes are the two most promising high-capacity anodes for the next-generation battery design due to extremely high lithium-storage capacities and low working potentials. Pairing these two anodes with high-voltage cathodes promi...[ Read more ]

Li-ion batteries (LIBs) have become the pivotal nexus for energy storage in the modern society. With the rapid development of electric vehicles (EVs), the fast growth of grid-scale energy storage, and a surge of novel applications, batteries with higher specific energies are urgently demanded. Unfortunately, the state-of-the-art LIBs offer energy densities below 250 Wh kg^-1, unable to support application scenarios like ultralong-range EVs, drones, or flying cars, which require batteries with a specific energy of above 350 Wh kg^-1. Silicon anodes or lithium-metal anodes are the two most promising high-capacity anodes for the next-generation battery design due to extremely high lithium-storage capacities and low working potentials. Pairing these two anodes with high-voltage cathodes promises high specific energies. Nevertheless, the dendrite issue of lithium metal, the large volume variation of silicon anodes, the oxidation of electrolytes, the crack and dissolution of cathodes seriously block the commercialization of silicon-based LIBs or rechargeable lithium-metal batteries (LMBs). To fully tackle the abovementioned issues, designing advanced electrolytes with desired physicochemical properties that simultaneously stabilize the high-capacity anodes and high-voltage cathodes is indispensable. In addition, appropriate structure designs further enhance the anode stability, thereby increasing the cycling lifespan of batteries.

We begin with modulating solid electrolyte interphases (SEIs) of silicon and lithium-metal anodes by a localized high concentration electrolyte. An entirely new lightweight and low-cost fluoride, benzotrifluoride, is proposed as diluent for electrolytes. The benzotrifluoride-diluted high-concentration electrolyte passivates the anodes by forming thin yet dense SEIs, promoting the reversibility of lithiation-delithiation process and avoiding the loss of active materials. Besides, this electrolyte enables stable cathode operation under 4.6 V. Pragmatic pouch cells based on silicon and lithium-metal demonstrate high specific energies of 257.4 and 349.4 Wh kg^-1, respectively.

To acquire high-performance LMBs with medium salt concentrations, we propose to utilize ethylene glycol dibutyl ether (EGDE) for preparing weakly solvating electrolytes. The EGDE with medium salt concentrations create rich contact ion pairs and ionic aggregates, enabling the stable operation of the Li-metal and high-voltage cathodes. The 4.4 V-class lithium-metal║NCM622 cell with the 3.5 mAh cm^-2 cathode and an anode-to-cathode ratio (N/P ratio) of 2.85 operates steadily for 180 cycles.

To realize ultrahigh voltage LMBs (> 4.5 V) with medium-to-low salt-to-solvent ratios, we developed a solvent molecule reconstruction strategy by highly controllable polymerization of 1,3-dioxolane (DOL). The polymerization process eradicates free solvents and transforms them into oxidation-proof polymerized DOL. The tailored solvation structures of electrolyte render the LiF-rich anode SEI and cathode electrolyte interphase (CEI), leading to the highly reversible lithium-metal anode, crack-free cathodes, and the thus longevity of full cells. Based on the designed electrolyte, the pouch LMB operating with the 4.6 V cutoff voltage delivers a high energy density of 346.6 Wh kg^-1.

To support the stable operation of the micron-sized silicon anode that is less costly and more pragmatic for commercialization compared to nanosized silicon anode. LiPF₆-in-EGDE electrolytes are designed to construct fluoride-rich and stratified SEIs. With this electrolyte, the micron-sized silicon anode stably operates at 0.5 A g^-1, maintaining a high capacity of 1901 mAh g^-1 after 500 cycles and showing the high operating Coulombic efficiency (CE) of 99.92%.

To further enhance the macroscopic structural stability and electrochemical performance of silicon anodes, the electrostatic self-assembly strategy is proposed for facile, efficient, and large-scale synthesis of silicon-based anodes. The two-dimensional MXene (Ti₃C₂X_n, X= F, O, OH, etc.) automatically assembles with silicon particles in aqueous solutions, forming honeycomb-like composites that demonstrate substantially improved rate and cycling performances.

Key words: Li-ion batteries; rechargeable Li-metal batteries; high concentration electrolyte; weakly solvating electrolyte; silicon anodes.