Novel Cathode Material for Rechargeable Lithium–Sulfur Batteries

This article describes the synthesis and characterization of a novel crosslinked polymer with tricyanuric acid core bearing tetrasulfide bridges as a novel redox polymerization electrode material for rechargeable lithium–sulfur batteries. The new material was synthesized by reaction of stoichiometric sulfur monochloride amounts with trithiocyanuric acid and the structure of the redox polymer proven by the means of elementary analysis, infrared spectroscopy and Raman spectroscopy. Electrochemical evaluation of the polymer as electroactive cathode component showed cycling stability up to 140 cycles after initial capacity of 650 mAhg–1 with 73% utilization of the theoretical specific capacity (893 mAhg–1) regarding the electroactive tetrasulfide moieties. Cell operation with excess amounts of electrolyte did not accelerate the cell degradation, indicating that the reduced sulfur species such as lower polysulfides (Li2S, Li2S2) and tris lithium salt of trithiocyanuric acid are efficiently immobilized on the cathode side

Improved performance of LiNi0.5Mn1.5O4 cathodes with electrolytes containing dimethylmethylphosphonate (DMMP)

The cycling performance of Li/LiNi0.5Mn1.5O 4 cells with 1.0 M LiPF6 in ethylene carbonate (EC)/ethyl methyl carbonate (EMC) (3:7) with and without added dimethyl methylphosphonate (DMMP) (0.5-1.0%) was investigated. Addition of DMMP resulted in improved capacity retention during cycling to high voltage (4.9 V vs Li). Ex-situ surface analysis of LiNi0.5Mn1.5O4 electrodes after cycling via Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and Infrared (IR) spectroscopy suggest that addition of DMMP inhibits electrolyte decomposition on the surface of the cathode. Addition of DMMP also inhibits the dissolution of Mn from LiNi0.5Mn1.5O 4 particles stored in electrolyte at 85 °C. © 2012 The Electrochemical Society

Studies of lithium-exchanged nafion as an electrode binder for alloy negatives in lithium-ion batteries

The use of lithium-exchanged Nafion as a polymer binder for alloy negative electrodes in lithium-ion batteries is demonstrated. Commercial Nafion solution was ion exchanged with LiOH in order to remove the mobile protons and prepare the lithium-containing polymer. The resulting Li-Nafion solution, crystalline silicon, and carbon black were used to prepare composite electrodes having final proportions of 8% binder, 80% silicon, and 12% carbon by weight, respectively. The prepared electrodes gave reversible specific capacities ranging from 800 to nearly 1000 mAh/g when cycled between 0.9 and 0.17 V. The capacity retention of the investigated electrode samples was very good, suggesting that lithium-exchanged Nafion is a promising binder for alloy negative electrodes of Li-ion batteries. (C) 2008 The Electrochemical Society

Surface phenomena of high energy Li(Ni1/3Co1/3Mn 1/3)O2/graphite cells at high temperature and high cutoff voltages

Layered Li(Ni1/3Co1/3Mn1/3)O2 (NCM) materials have been investigated at high working potential and elevated temperature to correlate electrochemical performance with changes to the electrode interface. Graphite/NCM cells were cycled to either 4.2 or 4.5 V vs Li/Li+ at room temperature (25 °C) followed by moderately elevated temperature (55 °C). Cells cycled to 4.2 and 4.5 V have similar capacity retention, but the cells cycled to 4.5 V have poorer first cycle efficiency, efficiency upon cycling at 55 °C, and greater increases in cell resistance. Surface analyses indicate thicker surface films on the cathode after cycling to 4.5 V, compared to cycling at a lower voltage of 4.2 V. The thicker surface film on the cathode is the result of electrolyte oxidation to generate poly(ethylene carbonate) and lithium alkyl carbonates. Electrochemical impedance spectroscopy of three-electrode cells reveals that the cathode dominates the cell impedance and the cathode impedance is much greater for cells cycled to 4.5 V than cells cycled to 4.2 V. © 2014 Elsevier B.V. All rights reserved

Failure Mechanism of Graphite/LiNi0.5Mn1.5O4 Cells at High Voltage and Elevated Temperature

The failure mechanism of graphite/LiNi0.5Mn1.5O4 cells cycled at 25°C and 55°C have been analyzed by electrochemical methods and ex-situ surface analysis of the electrodes. Graphite/LiNi0.5Mn1.5O4 cells cycle well at 25°C, but have rapid capacity fade upon cycling at 55° C. Independent electrochemical analysis of anodes and cathodes extracted from cells cycled at 55° C suggest that both electrodes have significant capacity loss, although the cathode capacity can be recovered with longer charging times. Ex-situ surface analysis of the cathode with SEM reveals that the bulk cathode particles and the cathode laminate are retained while XPS confirms the presence of a cathode electrolyte interface composed of the decomposition products of the electrolyte. Ex-situ analysis of the anode reveals a thick anode solid electrolyte interphase (SEI), anode delamination, and the presence of Mn. The results suggest that both the anode and the cathode contribute to performance loss in graphite/LiNi0.5Mn1.5O4 cells. © 2013, The Electrochemical Society, Inc. All rights reserved

Improving the performance of graphite/LiNi0.5Mn 1.5O4 cells at high voltage and elevated temperature with added lithium Bis(oxalato) borate (LiBOB)

The performance of the graphite/LiNi0.5Mn1.5O 4 cells cycled to 4.8 V (vs Li/Li+) with 1.0MLiPF6 in EC/EMC (3/7, v/v) with and without added LiBOB (1.5 and 2.5% (wt)) at 25 and 55?C has been investigated. The initial discharge capacity of the cells with added LiBOB is slightly lower than the cells without added LiBOB. However, after 30 cycles at 55?C, the cells with standard electrolyte suffer poor capacity retention (20%). The cells with 1.5% or 2.5% LiBOB have good cycling stability at 55?C with 63 and 69% capacity retention, respectively, after 30 cycles. The cells containing added LiBOB also have better coulombic efficiency and lower impedance after cycling at 55?C. Ex-situ surface analysis of both the anode and the cathode extracted from graphite/LiNi0.5Mn1.5O4 cells was conducted via a combination of XPS, SEM, TEM with EDX, and ICP-MS. The improved cycling performance with added LiBOB can be attributed to the inhibition of electrolyte decomposition at the electrode surfaces and inhibition of Mn and Ni dissolution from the cathode and deposition on the anode upon cycling at high voltage and elevated temperature. © 2013 The Electrochemical Society

The Use of Redox Mediators for Enhancing Utilization of Li₂S Cathodes for Advanced Li–S Battery Systems

The development of Li₂S electrodes is a crucial step toward industrial manufacturing of Li–S batteries, a promising alternative to Li-ion batteries due to their projected two times higher specific capacity. However, the high voltages needed to activate Li₂S electrodes, and the consequent electrolyte solution degradation, represent the main challenge. We present a novel concept that could make feasible the widespread application of Li₂S electrodes for Li–S cell assembly. In this concept, the addition of redox mediators as additives to the standard electrolyte solution allows us to recover most of Li₂S theoretical capacity in the activation cycle at potentials as low as 2.9 V_Li, substantially lower than the typical potentials >4 V_Li needed with standard electrolyte solution. Those novel additives permit us to preserve the electrolyte solution from being degraded, allowing us to achieve capacity as high as 500 mAhg^–1_Li₂S after 150 cycles with no major structural optimization of the electrodes