Introducing nonvolatile liquid acids into porous solids is a promising solution to construct anhydrous proton-conducting electrolytes, but due to weak coordination or covalent bonds building these solids, they often suffer from structural instability in acidic environments. Herein, we report a series of steady conjugated microporous polymers (CMPs) linked by robust alkynyl bonds and functionalized with perfluoroalkyl groups and incorporate them with phosphoric acid. The resulting composite electrolyte exhibits high anhydrous proton conductivity at 30−120 °C (up to 4.39 × 10 −3 S cm −1 ), and the activation energy is less than 0.4 eV. The excellent proton conductivity is attributed to the hydrophobic pores that provide nanospace for continuous proton transport, and the hydrogen bonding between phosphoric acid and perfluoroalkyl chains of CMPs promotes short-distance proton hopping from one side to the other.
Poly(ethylene
glycol) (PEG)-derived electrolytes can promote not
only conduction of lithium ions but also that of anions. To avoid
anion conduction and increase the Li-ion transference number, we propose
a new concept that utilizes crowded space to restrict anion movement.
Branched PEG chains with different lengths were covalently grafted
into the pore surface of covalent organic frameworks (COFs) and construct
crowded nanochannels. After incorporating LiTFSI, the COF with longer
PEG chains achieves an ionic conductivity of 1.5 × 10–3 S cm–1 at 200 °C and an activation energy
of 0.60 eV. It also inhibits anion movement in a certain direction
and obtains a higher transference number than other COFs with shorter
PEG chains. The full cell is further assembled, finally obtaining
a specific discharge capacity of 153 mAh g–1 after
60 cycles at 100 °C.
Covalent organic frameworks (COFs) are attractive candidates for Li + -conducting electrolytes owing to their regular channels and tailored functionalities. However, most COF electrolytes are employed at high temperatures, challenging their practical use. Herein, tailored COFs coupled with PEG composite electrolytes were designed to construct a flowable network for facilitating Li + transport at lower temperatures. Benefiting from the interaction between the rigid COF structure and flowing PEG chain, the ionic conductivity of the quasi-solid electrolytes reached 9.74 × 10 −7 S cm −1 (−40 °C), 7.10 × 10 −5 S cm −1 (0 °C), and 1.36 × 10 −3 S cm −1 (80 °C). The resultant LiFePO 4 |Li cell delivered a discharge specific capacity of 132.5 mAh g −1 after 80 cycles at 10 °C. The Li−Li symmetrical cell displayed a long-time operation stability of over 800 h when cycled at a low temperature (10 °C). This work opens a new avenue to broaden the practical application of COFs electrolytes in quasi-solid lithium-ion batteries.
The
ion aggregation induced by a strong Coulomb force leads to
hard charge separation and poor proton conductivity. Herein, covalent
organic frameworks (COFs) linking both positive charged imidazole
and negative charged sulfonic acid were produced and were finally
incorporated with NH4Br molecules. As a result, the charge
separation ability of NH4Br molecules is profoundly enhanced
by charged groups on COFs, which is proved by X-ray photoelectron
spectroscopy measurement. The proton conductivity of charged COFs
is higher than that of neutral COFs, which can be as high as 3.7 ×
10–3 S cm–1 at 90 °C and
100% relative humidity. The activation energy is also lower in charged
COFs, demonstrating strengthened charge separation ability and easier
moving proton carriers as well.
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