隔膜对双电层电容器和混合型电池-超级电容器的电化学性能的影响

隔膜是双电层电容器和混合型电池-超级电容器等电化学储能器件的重要组成元件.本文采用1 mol?L-1四乙基四氟硼酸铵的丙烯碳酸酯电解液制备了基于活性炭的扣式双电层电容器,并采用1 mol?L-1六氟磷酸锂锂离子电解液制备了(LiNi0.5Co0.2Mn0.3O2+活性炭)/石墨体系的混合型电池-超级电容器.研究了不同类型隔膜的物理化学性能,以及其对双电层电容器和混合型电池-超级电容器的电化学性能的影响.四种隔膜分别是无纺布聚丙烯毡、多孔聚丙烯薄膜、Al2O3涂层的聚丙烯薄膜和纤维素纸隔膜.进行了表面形貌、差示扫描量热、电解液吸液量和表观接触角测试表征.电化学测试表明,采用纤维素隔膜的双电层电容器具有最高的比电容和更优的倍率性能,电容器的自放电性能差别不大.而对于混合型电池-超级电容器,采用聚丙烯薄膜和无纺布聚丙烯毡隔膜器件的比容量比其它器件约高20%,且采用纤维素隔膜的器件自放电率最高.     

NaOH电解液改善MH/Ni电池自放电性能的机理研究

以NaOH电解液代替KOH能够明显改善MH/N i电池的自放电性能和高温(60℃)充电效率.电化学阻抗和循环伏安测试表明,NaOH电解液的作用可能是改变了H原子于负极表面的吸(脱)附行为,并在一定程度上抑制了负极的析氢过程,从而改善了电池的自放电性能.     

Improvement of electrochemical properties of the spinel LiMn2O4 using a Cr dopant effect

A series of LiCr_xMn_2−xO₄ spinels were synthesised by the Pechini method which enables dopant Cr ions to distribute at Mn sites homogeneously. Neutron diffraction and EDS analysis confirmed that Cr ions do occupy 16d sites (octahedral intestial) evenly in the spinel structure. The Cr dopant effect improves the cyclability of spinel LiMn₂O₄ electrodes and decreases the self-discharge rate substantially. Cyclic voltammetry and AC impedance spectroscopy were employed to characterise the reactions of lithium insertion into and extraction from LiCr_xMn_2−xO₄ electrodes. It was found that a thicker surface layer was formed on the surface of the pure LiMn₂O₄ electrode than on the LiMn₂O₄ electrode.     

Describing the unsuspected advantage of redox ionic liquids applied to electrochemical energy storage

Ionic liquids are a class of solvents widely studied in the literature for various applications. As a subclass of ionic liquids, redox ionic liquids can endow charge exchange properties (electrons transfer) to these electrolytes for electrochemical energy storage. In this review article, we propose to study this family of ionic liquids and suggest a chronological classification. We introduce five generations of redox ionic liquids with different basic compounds such as polyethylene glycol, ferrocene, different linker lengths, TFSI anion, and biredox ionic liquids. The versatility of the redox ionic liquids synthesis will be discussed as well as the fundamental and applied aspects of their use as electrolytes, which have high charge densities. The impact of the redox ionic liquids on the electrochemical mechanisms will be described. We also present how the redox shuttle effect, detrimental to supercapacitors, can be prevented while it can be used to improve lithium-ion batteries.     

N- and S-doped ordered mesoporous carbon tubes with efficient S confinement for high-performance Li–S batteries

The insulating properties of S/Li₂S₂/Li₂S and the soluble Li₂S₄/Li₂S₆/Li₂S₈ obstruct the practical application of Li–S batteries. In this work, highly ordered N and S co-doped mesoporous carbon tubes (NSMCTBs) with high specific surface areas and large pore volume are employed to confine and improve the utilization efficiency of S species in Li–S batteries. The strong S_nLi₂?N interaction and S–S chemical bond between thiophenic S and Li₂S_n guarantee the exceptional electrochemical performance of as-prepared NSMCTBs/S cathode. A relatively high discharge capacity of 1315.2 mAh g^?1 is achieved for the first cycle at 0.5 C and maintained at 644.1 mAh g^?1 after 500 cycles. The NSMCTBs/S with high S content of up to 80%, it also delivers a discharge capacity of 1092.1 mAh g^?1 and considerable cycling performance. More importantly, the NSMCTBs/S can effectively suppress the self-discharge behavior of Li–S batteries.     

Concurrently Increasing Specific Energy and Suppressing Self-Discharge of Electrochemical Capacitors by Complexing Carbon Nanotubes with Redox Active Units-Containing Charged Copolymers

Specific energy and self-discharge are two important performances of electrochemical capacitors. In this work, we have fabricated the composite electrodes by complexing the negatively charged carboxylated multi-walled carbon nanotubes (cMWCNT) with the redox active units-containing positively charged random copolymers. 2, 2, 6, 6-Tetramethylpiperidinyl-N-oxyl and viologen are employed as model redox active units to exemplify the strategy of the concurrent increase of specific energy and suppression of self-discharge of a two-electrode device. The slower hydrogen and oxygen evolution reactions compared with the reactions of the redox active units lead to an increased electrolyte decomposition window, thereby giving rise to an increase in specific energy. On the other hand, the complexation between the cMWCNT and the copolymers suppresses both the redox shuttling and the cross-diffusion of the redox active units-containing polymer chains, leading to an improved performance of self-discharge. Based on the complexation between carbon nanotubes and redox active units-containing charged copolymers, this work provides a convenient and universal strategy to concurrently increase specific energy and suppress self-discharge of electrochemical capacitors.