Cu foil

The following battery components were used: carbon black (Super C65, TIMCAL), carboxymethyl cellulose (CMC, Grade: 2200, Lot No. B1118282, Daicel Fine Chem Ltd.), NaClO₄ (98%, Alfa Aesar, additionally dried), propylene carbonate (BASF, battery grade), 4-fluoro-1,3-dioxolan-2-one (FEC, Hisunny Chemical, battery grade), glass microfiber separator (GF/D, Cat No.1823-257, Whatman), and Cu foil (9 μm, MTI Corporation).
In a typical electrode preparation, the respective materials were combined with deionized water and mixed in a Fritsch Pulverisette 7 classic planetary mill for 1 h at 500 rpm. Mixing weight ratios were Sb:CB:CMC = 64%:21%:15% for pure Sb NCs (Fig. 2), and P/Sb:CB:CMC = 40%:40%:20% or P/Sb:CB:Cu:CMC = 40%:30%:10%:20% (Fig. 3). The aqueous slurries were coated onto Cu current collectors and then dried overnight at 80°C under vacuum prior to use. All electrochemical measurements were conducted in homemade, reusable and air-tight coin-type cells assembled in an Ar-filled glove box (O₂ < 1 ppm, H₂O < 1 ppm). Elemental sodium was employed as both reference and counter electrode. As electrolyte 1 M NaClO₄ in propylene carbonate with 10% fluoroethylene carbonate was used. Glass fiber was used as separator. Galvanostatic cycling tests were carried out at room temperature on MPG2 multi-channel workstation (BioLogic). Capacities were normalized by the mass of active material.

Lithium hexafluorophosphate (LiPF₆), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 1,2-dimethoxyethane (DME), 1,3-dioxolane (DOL) and propylene carbonate (PC) (all in battery-grade purity) were obtained from BASF Corporation. Lithium bis(fluorosulfonyl)imide (LiFSI) was obtained from Nippon Shokubai and used as-received. The electrolytes were prepared by dissolving the desired amount of salt into the solvent. Li foil and Cu foil were purchased from MTI Corporation and All Foils, respectively. The materials were stored and handled in an MBraun LABmaster glove box with an Ar atmosphere (<1 p.p.m. O₂ and <1 p.p.m. H₂O).