Reduction-Tolerance Electrolyte Design for High-Energy Lithium Batteries.

Lithium batteries employing Li or silicon (Si) anodes hold promise for the next-generation energy storage systems. However, their cycling behavior encounters rapid capacity degradation due to the vulnerability of solid electrolyte interphases (SEIs). Though anion-derived SEIs mitigate this degradation, the unavoidable reduction of solvents introduces heterogeneity to SEIs, leading to fractures during cycling. Here, we elucidate how the reductive stability of solvents, dominated by the electrophilicity (EPT) and coordination ability (CDA), delineates the SEI formed on Li or Si anodes. Solvents exhibiting lower EPT and CDA demonstrate enhanced tolerance to reduction, resulting in inorganic-rich SEIs with homogeneity. Guided by these criteria, we synthesized three promising solvents tailored for Li or Si anodes. The decomposition of these solvents is dictated by their EPTs under similar solvation structures, imparting distinct characteristics to SEIs and impacting battery performance. The optimized electrolyte, 1 M lithium bis(fluorosulfonyl)imide (LiFSI) in N-Pyrrolidine-trifluoromethanesulfonamide (TFSPY), achieves 600 cycles of Si anodes with a capacity retention of 81 % (1910 mAh g-1). In anode-free Cu||LiNi0.5Co0.2Mn0.3O2 (NCM523) pouch cells, this electrolyte sustains over 100 cycles with an 82 % capacity retention. These findings illustrate that reducing solvent decomposition benefits SEI formation, offering valuable insights for the designing electrolytes in high-energy lithium batteries.

Ligand-channel-enabled ultrafast Li-ion conduction.

Li-ion batteries (LIBs) for electric vehicles and aviation demand high energy density, fast charging and a wide operating temperature range, which are virtually impossible because they require electrolytes to simultaneously have high ionic conductivity, low solvation energy and low melting point and form an anion-derived inorganic interphase1-5. Here we report guidelines for designing such electrolytes by using small-sized solvents with low solvation energy. The tiny solvent in the secondary solvation sheath pulls out the Li+ in the primary solvation sheath to form a fast ion-conduction ligand channel to enhance Li+ transport, while the small-sized solvent with low solvation energy also allows the anion to enter the first Li+ solvation shell to form an inorganic-rich interphase. The electrolyte-design concept is demonstrated by using fluoroacetonitrile (FAN) solvent. The electrolyte of 1.3 M lithium bis(fluorosulfonyl)imide (LiFSI) in FAN exhibits ultrahigh ionic conductivity of 40.3 mS cm-1 at 25 °C and 11.9 mS cm-1 even at -70 °C, thus enabling 4.5-V graphite||LiNi0.8Mn0.1Co0.1O2 pouch cells (1.2 Ah, 2.85 mAh cm-2) to achieve high reversibility (0.62 Ah) when the cells are charged and discharged even at -65 °C. The electrolyte with small-sized solvents enables LIBs to simultaneously achieve high energy density, fast charging and a wide operating temperature range, which is unattainable for the current electrolyte design but is highly desired for extreme LIBs. This mechanism is generalizable and can be expanded to other metal-ion battery electrolytes.

50C Fast-Charge Li-Ion Batteries using a Graphite Anode.

Li-ion batteries have made inroads into the electric vehicle market with high energy densities, yet they still suffer from slow kinetics limited by the graphite anode. Here, electrolytes enabling extreme fast charging (XFC) of a microsized graphite anode without Li plating are designed. Comprehensive characterization and simulations on the diffusion of Li+ in the bulk electrolyte, charge-transfer process, and the solid electrolyte interphase (SEI) demonstrate that high ionic conductivity, low desolvation energy of Li+ , and protective SEI are essential for XFC. Based on the criterion, two fast-charging electrolytes are designed: low-voltage 1.8 m LiFSI in 1,3-dioxolane (for LiFePO4 ||graphite cells) and high-voltage 1.0 m LiPF6 in a mixture of 4-fluoroethylene carbonate and acetonitrile (7:3 by vol) (for LiNi0.8 Co0.1 Mn0.1 O2 ||graphite cells). The former electrolyte enables the graphite electrode to achieve 180 mAh g-1 at 50C (1C = 370 mAh g-1 ), which is 10 times higher than that of a conventional electrolyte. The latter electrolyte enables LiNi0.8 Co0.1 Mn0.1 O2 ||graphite cells (2 mAh cm-2 , N/P ratio = 1) to provide a record-breaking reversible capacity of 170 mAh g-1 at 4C charge and 0.3C discharge. This work unveils the key mechanisms for XFC and provides instructive electrolyte design principles for practical fast-charging LIBs with graphite anodes.

Low-cost batteries based on industrial waste Al-Si microparticles and LiFePO4 for stationary energy storage.

Owing to their high capacity and low working potential, Si-based anodes are regarded as potential alternatives to graphite anodes to meet the higher requirements of Li-ion batteries (LIBs). However, high volume change causes the fracturing and pulverization of the bulk anode and continuous side reactions, which are more severe in large-particle Si anodes, limiting its practical application. Herein, to build a low-cost battery system, we chose a common industrial waste product, Al-Si microparticles (Al-SiMPs, ∼30 µm), as the anode for LIBs and coupled it with a 2.0 M LiFP6 2-MeTHF electrolyte to support its operation. The Al-SiMP anode showed a high specific capacity and a significantly improved electronic conductivity, ensuring high energy and power densities. An ultra-high initial coulombic efficiency (iCE) of 91.6% and a cycling CE of ∼99.9% were obtained in the half-cells, which delivered a capacity of 1300 mA h g-1 and maintained 95.3% after 100 cycles. Paired with low-cost and high-safety LiFePO4 as the cathode, the LFP||Al-SiMP full cells showed decent cycling stability and exhibited a considerable cost advantage, demonstrating a competitive solution for stationary energy storage.

A facile approach toward multifunctional polyethersulfone membranes via in situ cross-linked copolymerization.

In this study, multifunctional polyethersulfone (PES) membranes are prepared via in situ cross-linked copolymerization coupled with a liquid-liquid phase separation technique. Acrylic acid (AA) and N-vinylpyrrolidone (VP) are copolymerized in PES solution, and the solution is then directly used to prepare PES membranes. The infrared and X-ray photoelectron spectroscopy testing, scanning electron microscopy, and water contact angle measurements confirm the successful modification of pristine PES membrane. Protein adsorption, platelet adhesion, plasma recalcification time, and activated partial thromboplastin time assays convince that the modified PES membranes have a better biocompatibility than pristine PES membrane. In addition, the modified membranes showed good protein antifouling property and significant adsorption property of cationic dye. The loading of Ag nanoparticles into the modified membranes endows the composite membranes with antibacterial activity.