The incompatibility between the anode and the cathode chemistry limits the used of Mg as an anode. This issue may be addressed by separating the anolyte and the catholyte with a membrane that only allows for Mg2+ transport. Mg‐MOF‐74 thin films were used as the separator for this purpose. It was shown to meet the needs of low‐resistance, selective Mg2+ transport. The uniform MOF thin films supported on Au substrate with thicknesses down to ca. 202 nm showed an intrinsic resistance as low as 6.4 Ω cm2, with the normalized room‐temperature ionic conductivity of ca. 3.17×10−6 S cm−1. When synthesized directly onto a porous anodized aluminum oxide (AAO) support, the resulting films were used as a standalone membrane to permit stable, low‐overpotential Mg striping and plating for over 100 cycles at a current density of 0.05 mA cm−2. The film was effective in blocking solvent molecules and counterions from crossing over for extended period of time.
Polyoligomeric silsesquioxanes with eight (LiNSO2CF3) groups can be dissolved at very high loadings into tetraglyme, forming solvent-in-salt electrolytes, and stable colloids with increasing amount of tetraglyme. Li+ ions can migrate by diffusive or coordinated hopping motions. High tLi+ and conductivities are obtained.
Self-standing, high conductivity solid iongel electrolytes
with
good thermal stability (T
d ∼ 200
°C), mechanical properties, and an anodic stability up to 5 V
were prepared using the solvate ionic liquid [G4Li]+[TFSI]− in methyl cellulose (MC) with 90
wt % liquid. The excellent combination of high room temperature conductivity
(σ > 10–4) and storage modulus (E′ ∼ 60 MPa) is due to the semicrystalline
fibrillar
network formed by the MC. The high anodic stability of 5 V for the
iongel is attributed to the known 4.5 V stability of the [G4Li]+[TFSI]− and the −OH groups
on MC, which hydrogen bond with any free G4 not in the
[G4Li]+[TFSI]− complex, so
that they are unavailable for oxidation. Li0/iongel/Li0 plating/stripping at low current densities is stable with
low polarization, but at high current densities the polarization and
cell impedance increase, which is due to mosaic lithium plating. Coin
cells of Li0/iongel/LiFePO4 could be cycled
at C/2 (1C = 170 mA h/g) for at least 100 cycles with 98–99%
Coulombic efficiency and capacities of 125 mA h/g, comparable to that
of the pure liquid [G4Li]+[TFSI]− cells.
Solid ion-gel separators for lithium or lithium ion batteries have been prepared with high lithium ion transference numbers (tLi+ = 0.36), high room temperature ionic conductivities (σ → 10−3 S cm−1), and moduli in the MPa range.
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