Composite cathode for Li-sulfur system: Effect of inorganic additives on electrochemical performance

Abstract

The influence of five different inorganic additives with different composition and morphology, viz. nanofibrous rutile/TiOxNy, Li4Ti5O12 (LTS) from Altair, TiO2-P90 from Evonik, TiOxNy-anatase and nano-TiO2 on the electrochemical performance of the activated carbon/sulfur composite cathode is evaluated by cyclic voltammetry at the scan rate of 0.1 mV s-1 and by galvanostatic chronopotentiometry at the 0.1 C rate. The composites are prepared by facile mechanical mixing of activated carbon with the inorganic additive and subsequent melting-diffusion with sulfur. The addition of nano-TiO2 from titanium isopropoxide, TiOxNy-anatase, rutile/TiOxNy, and LTS Altair to the carbon/sulfur composite cathode increased the charge capacity of the corresponding Li-sulfur cell. The negative effect of the P90 additive can be attributed to the blocking of its surface by Al2O3 and SiO2, hindering the adsorption of polysulfides. TiOxNy-anatase additive exhibits the highest capacity improvement due to its surface-enhanced redox chemistry of conductive and sulphiphilic surface resulting in a 7 % increase of the voltammetric charge capacity. In addition, this additive has a beneficial effect on the cycling stability of the sulfur composite cathode during galvanostatic cycling.

High-entropy oxychloride increasing the stability of Li–sulfur batteries

“…Our previous works studying the effect of more common inorganic additives (TiO 2 ) on the performance of the sulfur/carbon composite cathode evidenced just their contribution to the charge capacity increase. 29,30,39 The long-term stability of the corresponding sulfur composite cathode was in all previous studies controlled exclusively by the carbonaceous additive. However, in contrary to LiHEOFeCl, which is electrochemically inactive in the Li–sulfur battery potential window (1.7 V/2.9 V), see above, the previously studied inorganic additive (TiO 2 ) exhibited an inherent electrochemical activity within the operating potential window of the Li–sulfur system.…”

“…Although this capacity drop between particular cycles of the LiHEOFeCl-free composite cathode declines with progressive cycling, the corresponding charge capacities are signicantly lower than those of the P_carbon_LiHEOFeCl_sulfur cathode. The charge capacity increase ascribed to the LiHEOFeCl additive is superior as compared to that of other additives (nano TiO 2 , Li 4 Ti 5 O 12 or TiN x O y ), 30 despite their much larger specic surface area. Obviously, the structural stability of the multicomponent LiHEOFeCl material resulting from its high entropy of mixing 41 Table 1 The comparison of the electrochemical parameters of the coin cells with a sulfur composite cathode containing pure P_carbon (data from ref.…”

“…Our recent studies conrmed the benecial effect of various inorganic additives on the capacity and cycling stability of the composite cathode in Li-sulfur batteries. 27,29,30 This paper aims to broaden the portfolio of promising inorganic additives for the composite cathode in Li-sulfur batteries by lithiated high-entropy oxychloride additive Li 0.5 (Zn 0.25 Mg 0.25 Co 0.25 -Cu 0.25 ) 0.5 Fe 2 O 3.5 Cl 0.5 (LiHEOFeCl) and to evaluate its effect on the electrochemical behavior of the system. To the best of our knowledge, there are only few papers reporting the use of highentropy oxides in Li-sulfur batteries, 31,32 but none of them evaluated the inherent electrochemical activity of high-entropy material within the potential window of the Li-sulfur battery.…”