Enhanced Li–S Batteries Using Amine-Functionalized Carbon Nanotubes in the Cathode

Abstract

The rechargeable lithium-sulfur (Li-S) battery is an attractive platform for high-energy, low-cost electrochemical energy storage. Practical Li-S cells are limited by several fundamental issues, including the low conductivity of sulfur and its reduction compounds with Li and the dissolution of long-chain lithium polysulfides (LiPS) into the electrolyte. We report on an approach that allows high-performance sulfur-carbon cathodes to be designed based on tethering polyethylenimine (PEI) polymers bearing large numbers of amine groups in every molecular unit to hydroxyl- and carboxyl-functionalized multiwall carbon nanotubes. Significantly, for the first time we show by means of direct dissolution kinetics measurements that the incorporation of CNT-PEI hybrids in a sulfur cathode stabilizes the cathode by both kinetic and thermodynamic processes. Composite sulfur cathodes based the CNT-PEI hybrids display high capacity at both low and high current rates, with capacity retention rates exceeding 90%. The attractive electrochemical performance of the materials is shown by means of DFT calculations and physical analysis to originate from three principal sources: (i) specific and strong interaction between sulfur species and amine groups in PEI; (ii) an interconnected conductive CNT substrate; and (iii) the combination of physical and thermal sequestration of LiPS provided by the CNT=PEI composite.

The Effective Design of a Polysulfide-Trapped Separator at the Molecular Level for High Energy Density Li–S Batteries

“…Obviously, the new peaks appear after cycles at around 620 and 1050 cm -1 , which are corresponding to the N-Li and C-S bonds, respectively. 28,40 Therefore, the XPS result combining with the FT-IR spectra explicitly certify the chemical bonds formed between g-C 3 N 4 and LiPSs. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 cycling also block the electron and ion channel and decrease the accessibility of active material.…”

Highly Conductive, Sulfonated, UV-Cross-Linked Separators for Li–S Batteries

“…[13][14][15] Very recently it was shown that when such additives are engineered to form physical and covalent-like chemical bonds with LiPS, they are particularly effective in providing physical barriers and thermal constraints for preventing LiPS loss to the electrolyte at equilibrium. 16,17 However, detailed studies show that even in these favorable situations there is always a certain amount of LiPS that dissolves into the electrolyte during battery cycling. 16 While this inevitable LiPS loss from the cathode might be small enough at equilibrium to be ignored from the perspective of loss of active material and capacity over time, the high reactivity of LiPS with the Li anode drives cell failure by simultaneously depleting LiPS from the electrolyte, which drives additional loss, and passivation of the lithium metal surface which increases the cell overpotential during recharge, leading to additional modes of failure such as electrolyte decomposition and Li dendrite formation at the anode.…”

An integrally-designed, flexible polysulfide host for high-performance lithium-sulfur batteries with stabilized lithium-metal anode

“…The ACNF@MnO 2 electrode without CNT suffers from poor rate capability due to slow electron and ion transport ( Figure S8). Figure S9) [42,43]. The discharge plateaus correspond to the reduction of elemental sulfur to high-order polysulfides and then to Li 2 S/Li 2 S 2 , while the charge plateaus represent the reverse process ( Figure S10) [44].…”