Long Cycle Life Organic Polysulfide Catholyte for Rechargeable Lithium Batteries

Abstract

Organic compounds with active sites for lithiation can be used as electrode materials for lithium batteries. Their tunable structures allow a variety of materials to be made and investigated. Herein, a spectrum of dipyridyl polysulfides (Py2Sx, 3 ≤ x ≤ 8) is prepared in electrolyte by a one‐pot synthesis method from dipyridyl disulfide (Py2S2) and elemental sulfur. It renders up to seven dipyridyl polysulfides (i.e., Py2S3, Py2S4, Py2S5, Py2S6, Py2S7, and Py2S8) which show fully reversible electrochemical behavior in lithium batteries. In the discharge, the initial lithiation occurs at 2.45 V leading to the breakage of SαSβ bonds in Py2Sx and formation of lithium 2‐pyridinethiolate, in which lithium is coordinated in between N and S atoms. The left sulfur species act as elemental sulfur, showing two voltage plateaus at 2.3 and 2.1 V. The molecular dynamics simulations show the attraction between pyridyl groups and lithium polysulfides/sulfide via N···Li···S bonds, which enable good retention of soluble discharge products within electrodes and stable cycling performance. In the recharge, low‐order Py2Sx (e.g., Py2S3, Py2S4, and Py2S5) remain as the charged products. The mixture catholyte exhibits superlong cycle life at 1C rate with 1200 cycles and 70.5% capacity retention.

Aminomethyl‐Functionalized Carbon Nanotubes as a Host of Small Sulfur Clusters for High‐Performance Lithium–Sulfur Batteries

“…At a low lithiation degree of Li/S=0.4, the sequential binding energy per Li atom is −1.77 eV, accompanied by initial S−S bond breakage (mainly in the middle of the polysulfide chain). With an increase of the lithiation degree to Li/S=1.6, the sequential binding energy per Li atom fluctuates slightly between −1.4 and −1.9 eV, which corresponds to the reduction of the composite as AM‐CNT‐6 S 5 ‐AMCNT+48 e+48 Li→AM‐CNT‐6 (Li 2 S) 3 ‐6 (LiS) 2 ‐AMCNT, which is consistent with the situation reported recently . All the S−S bonds in the discharge products of Inter‐AM‐CNT‐6 S 5 (Li/S=1.6) broke and reformed to make 18 Li 2 S species (two‐electron transfer redox reaction) accompanied with the formation of 12 LiS species (one‐electron transfer redox reaction).…”

“…Generally, the discharge products of Li x S y species form a tight cluster structure and combine with the AM‐CNT skeleton through N⋅⋅⋅S⋅⋅⋅Li bridges to stabilize the whole system, similar to the cluster structures of the discharge products of organopolysulfide‐containing N‐heterocycles . Moreover, the unbroken N−S covalent bonding implies that the cross‐linked structure can be regenerated (which might be slightly different from the initial product) during the delithiation process and thus lead to a good cycling stability, similar to previous results . Combined with the superior structural stability of Inter‐6 S 5 ‐AM‐CNT discussed above, we suggest that the AM‐CNT cathode may show good reversibility during the charge and discharge processes.…”

“…From the above discussion, we suggest that the most favorable n and maximum n for a stable S n ‐AM‐CNT cathode might be 5 (which corresponds to a sulfur loading of 44.3 %) and 6 (which corresponds to a sulfur loading of 48.8 %), respectively. Even though the AM‐CNT composites based on high‐order sulfur are present in the initial cathode, they might be difficult to regenerate in the cycling process, similar to the situation of an organopolysulfide‐based cathode reported recently …”

“…According to the above discussion, the 48 Li‐Inter‐6 S 5 ‐AM‐CNT composite can be regarded as the fully lithiated configuration with a theoretical capacity of 1337 mA h g −1 (based on sulfur) or 592 mA h g −1 (based on the cathode), which is comparable with other cathodes based on small sulfur clusters . Moreover, the theoretical capacity can be further enhanced if Inter‐6 S 6 ‐AM‐CNT with high‐order S 6 clusters forms during the production of the cathode.…”

Organosulfide‐Based Deep Eutectic Electrolyte for Lithium Batteries

“…In our recent work, 2,2'-dipyridyl disulfide (DpyDS) was reported as an attractive cathode material in lithium batteries and exhibited excellent cycling performance. [9] The existence of Li•••N interaction on pyridine moieties significantly influences the cycling performance and electrochemical redox mechanism of DpyDS. Its believed that the Li•••N interaction, which has a similar mechanism with Li•••O interactions, can also induce the deep eutectic effect between DpyDS and LiTFSI.…”