Simultaneous Monitoring of Crystalline Active Materials and Resistance Evolution in Lithium–Sulfur Batteries

Abstract

Batteries. ChemRxiv. Preprint. Operando X-ray diffraction (XRD) is a valuable tool for studying secondary battery materials as it allows for the direct correlation of electrochemical behavior with structural changes of crystalline active materials. This is especially true for the lithium-sulfur chemistry, in which energy storage capability depends on the complex growth and dissolution kinetics of lithium sulfide (Li2S) and sulfur (S8) during discharge and charge, respectively. In this work, we present a novel development of this method through combining operando XRD with simultaneous and continuous resistance measurement using an Intermittent Current Interruption (ICI) method. We show that a coefficient of diffusion resistance, which reflects the transport properties in the sulfur/carbon composite electrode, can be determined from analysis of each current interruption. Its relationship to the established Warburg impedance model is validated theoretically and experimentally. We also demonstrate for an optimized electrode formulation and cell construction that the diffusion resistance increases sharply at the discharge end point, which is consistent with the blocking of pores in the carbon host matrix. The combination of XRD with ICI allows for a direct correlation of structural changes with not only electrochemical properties but also energy loss processes at a non-equilibrium state, and therefore is a valuable technique for the study of a wide range of energy storage chemistries. File list (2) download file view on ChemRxiv Manuscript.docx (3.06 MiB) download file view on ChemRxiv Supporting Information.pdf (720.53 KiB)

A fast alternative to the galvanostatic intermittent titration technique

“…This linear relationship of = O8/ has been demonstrated in previous work. 9 Above 3.7 V, the k values determined by ICI and GITT with 5-40 s interval are close to each other, which confirms the theoretical derivation in section 2.2 and is corroborated by the EIS results. The GITT results collected from the 50-150 s interval show higher k values and two local maxima between 3.7 and 4.2 V while the k values from other three analyses fluctuate less and are more consistent with each other.…”

“…Figure 2 displays the k values, which are √ ⁄normalized by the current (Equation18) from GITT and ICI, and the Warburg coefficients (σ) multiplied by O8/ from EIS fittings. This linear relationship of = O8/ has been demonstrated in previous work 9. Above 3.7 V, the k values determined by ICI and GITT with 5-40 s interval are close to each other, which confirms the theoretical derivation in section 2.2 and is corroborated by the EIS results.…”

Poly(ethylene Glycol-Block-2-Ethyl-2-Oxazoline) as Cathode Binder in Lithium-Sulfur Batteries

“…R corresponds to the sum of electronic, solution and charge transfer resistances, [36] while k characterizes the transport properties in the porous positive electrode. [37] In the resistance plots of the 10 th discharge, it can be observed that R of PO2k-212 is significantly higher than that of the other cells on the lower plateau (Q = 300-1000 mAh gS -1 ) while k is only slightly higher. This substantial difference was reproduced in repeated experiments with this binder, as shown in Fig.…”

“…The cells were rested for 6 h before discharged at C/50 (1C = 1672 mA gS −1 ) to 1.9 V and charged at C/25 to 2.6 V. After the formation cycle, the cell was cycled at C/10 between 1.8 and 2.6 V with a 1 s current pause every 5 min for the resistance measurement by the Intermittent Current Interruption (ICI) method. [36,37] Each discharge and charge step was limited to 10 h (time required to discharge/charge a cell with the theoretical capacity) to stop infinite discharging/charging (mostly charging) cause by polysulfide shuttling. The cells were tested on an Arbin BT-2043 battery testing system.…”

Nonpolar Solvent‐based Electrolytes with a Quasi‐Solid‐State Redox Reaction for Lithium‐Sulfur Batteries

“…[10][11][12][13][14] Moreover, the dissolved polysulfides form passivation layers on the cathode and anode surfaces, which give rise to an increase in cell polarization, resulting in the failure of LiÀ S cells. [15][16][17][18][19] Extensive efforts, such as sulfur-confined porous carbons, [20][21][22][23][24][25][26][27] electrolyte additives, [28,29] polysulfide adsorbents, [30][31][32][33] and small sulfur molecules, [22,34] have been devoted to overcoming these challenges. These approaches show promise for LiÀ S batteries, though their electrochemical performances are still not sufficient for practical usage.…”