Earth-abundant,layered birnessite is promising cathode for electrochemical capacitors due to the presence of confined nanofluids in interlayers for rapid ion storage.Previous work has demonstrated the capacitive co-in...Earth-abundant,layered birnessite is promising cathode for electrochemical capacitors due to the presence of confined nanofluids in interlayers for rapid ion storage.Previous work has demonstrated the capacitive co-intercalation of water and K+ions into birnessite in aqueous electrolytes,but in-depth quantitative investigations of the interactions between confined water and an external organic electrolyte are still lacking.In this work,we reveal the intercalation pseudocapacitance of hydrated birnessite(Na_(0.4)MnO_(2)·0.53H_(2)O)in sodium-based organic electrolytes via operando electrochemical quartz crystal microbalance(EQCM),and ex situ X-ray diffraction and Raman spectroscopy.The Na+ions are completely desolvated at the Na_(0.4)MnO_(2)·0.53H_(2)O-organic electrolyte interfaces and intercalate into the interlayers,while the confined water does not co-extract.The net Na+intercalation is a pseudocapacitive behavior without phase changes,displaying a high capacitive contribution of 85.6%at 1.0 m V/s.Additionally,EQCM results indicate the contributions of cation-dominated electric double layer(EDL)adsorption to the total charge storage.By replacing different solvents and anions in sodium-based organic electrolytes,we verify that Na+pseudocapacitive intercalation dominates the charge storage properties.展开更多
Relieving the stress or strain associated with volume change is highly desirable for high-performance SiOx anodes in terms of stable solid electrolyte interphase(SEI)-film growth.Herein,a Si-valence gradient is optimi...Relieving the stress or strain associated with volume change is highly desirable for high-performance SiOx anodes in terms of stable solid electrolyte interphase(SEI)-film growth.Herein,a Si-valence gradient is optimized in SiOx composites to circumvent the large volume strain accompanied by lithium insertion/extraction.SiO_(x)@C annealed at 850℃ has a gentle Si-valence gradient along the radial direction and excellent electrochemical performances,delivering a high capacity of 506.9 mAh g^(−1) at 1.0 A g^(−1) with a high Coulombic efficiency of~99.8%over 400 cycles.Combined with the theoretical prediction,the obtained results indicate that the gentle Si-valence gradient in SiO_(x)@C is useful for suppressing plastic deformation and maintaining the inner connection integrity within the SiO_(x)@C particle.Moreover,a gentle Si-valence gradient is expected to form a stress gradient and affect the distribution of dangling bonds,resulting in local stress relief during the lithiation/delithiation process and enhanced Li-ion kinetic diffusion.Furthermore,the lowest interfacial stress variation ensures a stable SEI film at the interface and consequently increases cycling stability.Therefore,rational design of a Si-valence gradient in SiOx can provide further insights into achieving high-performance SiOx anodes with large-scale production.展开更多
基金supported by the National Natural Science Foundation of China(No.22179113)the Guangdong High-Level Innovation Institute Project(No.2021B0909050001)the Fundamental Research Funds for the Central Universities(No.20720230028)。
文摘Earth-abundant,layered birnessite is promising cathode for electrochemical capacitors due to the presence of confined nanofluids in interlayers for rapid ion storage.Previous work has demonstrated the capacitive co-intercalation of water and K+ions into birnessite in aqueous electrolytes,but in-depth quantitative investigations of the interactions between confined water and an external organic electrolyte are still lacking.In this work,we reveal the intercalation pseudocapacitance of hydrated birnessite(Na_(0.4)MnO_(2)·0.53H_(2)O)in sodium-based organic electrolytes via operando electrochemical quartz crystal microbalance(EQCM),and ex situ X-ray diffraction and Raman spectroscopy.The Na+ions are completely desolvated at the Na_(0.4)MnO_(2)·0.53H_(2)O-organic electrolyte interfaces and intercalate into the interlayers,while the confined water does not co-extract.The net Na+intercalation is a pseudocapacitive behavior without phase changes,displaying a high capacitive contribution of 85.6%at 1.0 m V/s.Additionally,EQCM results indicate the contributions of cation-dominated electric double layer(EDL)adsorption to the total charge storage.By replacing different solvents and anions in sodium-based organic electrolytes,we verify that Na+pseudocapacitive intercalation dominates the charge storage properties.
基金This study was supported by a grant from the National Natural Science Foundation of China(No.61804030)the Solar Energy Conversion&Energy Storage Engineering Technology Innovation Platform(No.2018L3006)the Fujian Natural Science Foundation for Distinguished Young Scholars(Grant No.2020J06042).
文摘Relieving the stress or strain associated with volume change is highly desirable for high-performance SiOx anodes in terms of stable solid electrolyte interphase(SEI)-film growth.Herein,a Si-valence gradient is optimized in SiOx composites to circumvent the large volume strain accompanied by lithium insertion/extraction.SiO_(x)@C annealed at 850℃ has a gentle Si-valence gradient along the radial direction and excellent electrochemical performances,delivering a high capacity of 506.9 mAh g^(−1) at 1.0 A g^(−1) with a high Coulombic efficiency of~99.8%over 400 cycles.Combined with the theoretical prediction,the obtained results indicate that the gentle Si-valence gradient in SiO_(x)@C is useful for suppressing plastic deformation and maintaining the inner connection integrity within the SiO_(x)@C particle.Moreover,a gentle Si-valence gradient is expected to form a stress gradient and affect the distribution of dangling bonds,resulting in local stress relief during the lithiation/delithiation process and enhanced Li-ion kinetic diffusion.Furthermore,the lowest interfacial stress variation ensures a stable SEI film at the interface and consequently increases cycling stability.Therefore,rational design of a Si-valence gradient in SiOx can provide further insights into achieving high-performance SiOx anodes with large-scale production.
