High-Performance Lithium-Ion Hybrid Supercapacitors Based on Lithium Salt/Imidazolium Ionic Liquid Electrolytes and Ni-Doped LiMn₂O₄ Cathode Materials

Abstract

In this work, we evaluate the effect of Ni-doping LiMn2O4 spinels, LiNi x Mn2–x O4 (0.01 ≤ x ≤ 0.10) on the performance of lithium-ion hybrid supercapacitors (Li-HSCs) based on a mixture of 1 M lithium bis­(trifluoromethanesulfonyl)­imide (LiTFSI) and a 1-ethyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide (EMITFSI) ionic liquid (IL) as the electrolyte and mesoporous carbon as the anode. Although the positive contribution of metal doping of lithium-ion insertion materials in the electrochemical properties is known for Li-ion batteries, this effect is little studied in battery/supercapacitor hybrid full cells based on these compounds, especially with the use of electrolytes based on ionic liquids at room temperature. This issue is addressed in the present work. Among all studied devices, the Li-HSC based on LiNi0.01Mn1.99O4 was able to deliver the highest energy density values, in the range of 21.7–40.9 W h kg–1. Also, the devices based on low nickel-content spinels (x ≤ 0.03) showed high performance with excellent cycling stability, being able to retain around 79–85% of its initial energy density after 1500 cycles of charge/discharge at 400 mA g–1.

Understanding the Effect of Al Doping on the Electrochemical Performance Improvement of the LiMn2O4 Cathode Material

“…To solve the above problems, partial replacement of Mn 3+ through chemical doping was used to increase the average oxidation state of Mn (higher than 3.5), which will well restrain the structural deformation caused by Jahn–Teller distortion and hence improve the cyclic performance of LiMn 2 O 4 . , Several transition-metal (TM) elements are proved to be effective for doping, such as Ni, Al, Cr, Mg, Cu, and so on. Among the above elements, Al has been reported to be one of the most favorable elements as it is nontoxic, abundant, less expensive, and lighter than other TM elements. − Also, the chemical bond of Al–O (512 kJ mol –1 ) is stronger than that of Mn–O (402 kJ mol –1 ), so Al substitution will lead to the lattice parameter decrease and further increase the stability of octahedral sites by inhibiting the Jahn–Teller distortion .…”

Alkali and alkaline earth metals in liquid salts for supercapatteries

“…47 The same research group also investigated the performance of a Ni-doped LiMn 2 O 4 positrode in supercapatteries with a lithium salt/imidazolium IL electrolyte. 48 Fleischmann et al 32 used Li 4 Ti 5 O 12 as the negatrode, activated carbon as the positrode, and an IL containing Li salt as the electrolyte to form a supercapattery with a wide electrochemical window and a maximum voltage of 4.0 V. The reported EESD could achieve a specic energy of 100 W h kg −1 and a specic power of 2 kW kg −1 (Fig. 3).…”

“…47 The same research group also investigated the performance of a Ni-doped LiMn 2 O 4 positrode in supercapatteries with a lithium salt/imidazolium IL electrolyte. 48…”

Synthesis, characterization and study of electrochemical applicability of novel asymmetrically substituted 1,3-dialkyl-1,2,3-benzotriazolium salts for supercapacitor fabrication

“…Due to their unique electrochemical stability window, ILs effectively widen the operating voltage over 3.0 V. 13 They can effectively be used as electrolytes for critical energy storage applications like batteries and supercapacitors. [14][15][16][17] In spite of their different energy storage mechanisms, they have extended requirements for their electrolytes. Supercapacitors, by separating charges, store energy, while in batteries, electrochemical reactions are performed at electrodes.…”