Improvement of Cycle Capability of FeS₂Positive Electrode by Forming Composites with Li₂S for Ambient Temperature Lithium Batteries

Abstract

FeS 2 -Li 2 S composite positive electrode material, consisted of mainly Li 3 Fe 2 S 4 and Li 2.33 Fe 0.67 S 2 , was prepared for improving the cycle capability of FeS 2 in rechargeable lithium batteries with liquid electrolytes operated at ambient temperature. The electrochemical tests demonstrated that the FeS 2 -Li 2 S composite cells showed a relatively higher capacity retention after 15 cycles (ca. 64%) as compared with that of the FeS 2 cells (ca. 26%), though both sample cells showed comparable initial discharge capacities (ca. 740 and 790 mAh · g −1 (4.2 and 4.5 mAh · cm −2 ), respectively). The improved cycle capability of the FeS 2 -Li 2 S cells was ascribed particularly to rather unchanged discharge plateau at ca. 2.0 V, which was reported to correspond to the reduction of sulfur. The ex-situ S K-edge X-ray absorption fine structure measurements indicated that the redox reaction of sulfur ions (S 2 2− + 2e − ⇔ 2S 2− ), associated with Li extraction / insertion reactions, was still active after 15 cycles in the FeS 2 -Li 2 S electrode, while such redox reactions almost disappeared in the FeS 2 electrode. The atomic displacements required in the initial delithiation / lithiation were reduced in the FeS 2 -Li 2 S composite as compared with FeS 2 , which would give rise to the suppression of the structural irreversibility in the following charge / discharge, resulting in the improved cycle capability.

Understanding the degradation mechanism of rechargeable lithium/sulfur cells: a comprehensive study of the sulfur–graphene oxide cathode after discharge–charge cycling

“…For the initial S-GO composite cathode (0 cycle), several absorption features can be observed. According to the previous studies, 31,[36][37][38][39][40][41][42][43] the feature at 2472.2 eV can be attributed to the transition from the S 1s core level to the S-S p* states of elemental S or C-S-S-C p* states of S-GO, and the strong absorption feature at 2473.7 eV corresponds to the transition from the S 1s to the C-S s* of S-GO species. 36,37,42 The results can be confirmed by comparison of the TEY spectra of pure elemental S and S-GO, as shown in Fig.…”

“…The new peak at 2478.0 eV can be assigned to the transition of S 1s to S 2À s* and/ or SO 3 2À s*. 37,38 For the 2480.5 eV peak, at first thought it may appear to originate from the LiTFSI, the S K-edge of which shows a strong absorption peak at 2480.5 eV (see Fig. S2, ESI †), left on the cathode surface during sample preparation.…”

Preparation of Novel Electrode Materials Based on Lithium Niobium Sulfides

“…[1][2][3][4][5][6][7][8][9][10] However, because they do not contain lithium, their application to the positive electrode in cells with lithium-free negative electrode materials such as carbon or silicon-based alloys is limited.…”

“…4,5,7,8 Most of these electrodes charge and discharge at relatively low potentials, and thus are generally studied as negative electrodes. As a positive electrode material, composite materials comprising Li 2 S and transition metals (Fe, Cu, and Co) have been reported.…”

Electrochemical Mechanism for FeS2/C Composite in Lithium Ion Batteries with Enhanced Reversible Capacity

“…These nodes are chosen by analyzing several reports [23][24][25][26]. D1-2.0 V, D1-1.5 V and D1-1.0 V are the nodes in the initial discharge, whose voltages are 2.0 V, 1.5 V and 1.0 V, respectively.…”