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Poly(ethylene oxide)-coated sulfur/carbon (S/C/PEO) composite with a high sulfur loading is prepared to improve the performance of lithium-sulfur batteries. By magnetic string, 3.7 wt% PEO is coated onto the surface of ball-milling obtained S/C composite, leading to synthesis of S/C/PEO composite containing 78 wt% S. It is confirmed from a series of measurements that PEO covers the S/C composite uniformly, and PEO coating is quite effective in stabilizing the electrochemical performance. When employed as cathode for lithium-sulfur batteries, S/C/PEO delivers an initial discharge capacity of 989.6 mAh g and remains 648.3 mAh g after 110 cycles at a discharge/charge rate of 1 C (based on sulfur weight). Meanwhile, the coulomb efficiency of S/C/PEO composite reaches to ~98 % during the latter 105 cycles. The improved electrochemical performance can be attributed to the formation of PEO coating layer which can keep a tight contact between carbon and sulfur and lead to improved conductivity. Moreover, the PEO coating can act as a flexible cushion to accommodate volume changes of sulfur cathode as well as a barrier to trap soluble polysulfide intermediates during the charge-discharge processes. [ABSTRACT FROM AUTHOR]

Abstract: Efficient new extractant design relies on systematic structure–property studies. However, systematic structure–property research on extractants of organic phosphinic acids is far from sufficient. To make up for this deficiency, twelve organic phosphinic acid extractants (including nine dialkylphosphinic acids, two dicycloalkylphosphinic acids and one diarylphosphinic acid) were synthesized with free-radical-addition-reaction method and Grignard-reaction method. Reaction rules, advantages and disadvantages of these two methods were discussed respectively. The extraction ability and separation performance of the synthesized organic phosphinic acids for Tm, Yb and Lu from HNO3 solutions were evaluated and compared. For dialkylphosphinic acids the nearer the branched chain moved to P atom, the more reduction generated on the extraction ability. Dialkylphosphinic acids without branched chain in α-C or β-C (e.g. HYY-3, HYY-5, HYY-7 and HYY-9) exhibited strong extraction ability as P507. On the contrary, dialkylphosphinic acids with branched chain in α-C (e.g. HYY-4, HYY-8) and dicyclohexylphosphinic acids exhibited poor extraction ability as Cyanex 272. New compound Di-(2,3-dimethylbutyl)-phosphinic acid (HYY-2) exhibited good extraction ability and separation performance and its separation factors of Lu/Yb, Yb/Tm and Lu/Tm were 1.42, 3.10 and 4.40 respectively, apparently superior to Cyanex 272 (βLu/Yb =1.31, βYb/Tm =3.25, βLu/Tm =4.26). [Copyright &y& Elsevier]

The extraction and separation of heavy rare earths is always one of the most challenging unit operations in hydrometallurgy. Research and development of novel efficient extractant is one way to solve this problem. Organophosphinic acid is a good potential extractant. A new method was established for the synthesis of nonsymmetric dialkylphosphinic acid (NSDAPA) (R′R″POOH, R′ ≠ R″), optimized the synthesizing conditions of the key intermediate mono-alkylphosphinic acid and successfully synthesized three novel extractants ( n -octyl)(2,4,4′-trimethylpentyl) phosphinic acid, ( n -octyl)(cyclohexyl)phosphinic acid and (2,3-dimethylbutyl) (2,4,4′-trimethylpentyl)phosphinic acid. The extraction ability of the novel extractants was investigated. The structure–property relationship and the separation performance for heavy rare earth couples Er/Y, Y/Ho, Yb/Tm and Lu/Yb were evaluated. [ABSTRACT FROM AUTHOR]