Silicon is greatly promising for high-capacity anode materials in lithium-ion batteries (LIBs) due to their exceptionally high theoretical capacity. However, it has a big challenge of severe volume changes during charge and discharge, resulting in substantial deterioration of the electrode and restricting its practical application. This conflict requires a novel binder system enabling reliable cyclability to hold silicon particles without severe disintegration of the electrode. Here, a physically cross-linked polymer binder induced by reversible acid-base interaction is reported for high performance silicon-anodes. Chemical cross-linking of polymer binders, mainly based on acidic polymers including poly(acrylic acid) (PAA), have been suggested as effective ways to accommodate the volume expansion of Si-based electrodes. Unlike the common chemical cross-linking, which causes a gradual and nonreversible fracturing of the cross-linked network, a physically cross-linked binder based on PAA-PBI (poly(benzimidazole)) efficiently holds the Si particles even after the large volume changes due to its ability to reversibly reconstruct ionic bonds. The PBI-containing binder, PAA-PBI-2, exhibited large capacity (1376.7 mAh g(-1)), high Coulombic efficiency (99.1%) and excellent cyclability (751.0 mAh g(-1) after 100 cycles). This simple yet efficient method is promising to solve the failures relating with pulverization and isolation from the severe volume changes of the Si electrode, and advance the realization of high-capacity LIBs.
Low-temperature performance
of the rechargeable batteries is limited
because of a narrow temperature range of the electrolyte. Despite
the aqueous electrolyte having a lower freezing point than the ethelyenecarbonate
for conventional lithium-ion batteries, its freezing point is as high
as 0 °C. Antifreeze additive of ethylene glycol for aqueous electrolyte
solutions is used to improve the low-temperature performance of aqueous
rechargeable lithium-ion batteries. The suitable contents of ethylene
glycol expand the temperature range of aqueous electrolyte, pursuing
a balance between the low freezing point and high ionic conductivity,
and thus enhancing their cyclic performance and decreasing the polarization
of electrode reactions. Furthermore, the improvement of the lithium-ion
intercalation and deintercalation processes in the nano-LiFePO4 material at low temperature is controlled by varying the
content of the antifreeze additive to provide a high ionic conductivity
of an aqueous electrolyte solution having 1 M of Li2SO4 depending on the temperature, ranging from 0 to −20
°C. In addition, ethylene glycol for aqueous electrolyte solutions
can be used to improve high-performance batteries operating at sub-zero
temperatures. The aqueous rechargeable lithium-ion batteries having
antifreezing additives are beneficial for various extreme operations
of electric vehicles, high-altitude drones, submarine, robotics, and
aerospace applications.
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