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The effectiveness of three cyclic sulfate additives, ethylene sulfate (or 1,3,2-dioxathiolane-2,2-dioxide (DTD)), trimethylene sulfate (or 1,3,2-dioxathiane 2,2-dioxide (TMS)) and propylene sulfate (or 4-methyl-1.3,2-dioxathiolane-2,2-dioxide (PLS)) and one sulfonate additive, methylene methane disulfonate (1,5,2,4-dioxadithiane-2,2,4,4-tetraoxide (MMDS)) were studied in graphite/LiCoO2 (LCO) pouch cells. The additives were studied singly and in combination with 2% vinylene carbonate (VC) using high precision coulometry, AC impedance spectroscopy, volume change to infer gas evolution and open circuit storage experiments. During formation, TMS can significantly reduce the irreversible capacity and gas evolution while PLS and DTD cannot. When added alone, cells with DTD. TMS or PLS perform much worse than cells with 2% VC in all of coulombic efficiency, charge endpoint capacity slippage and voltage drop during storage. When combined with 2% VC, cells with TMS and VC provide similar performance to cells with 2% VC alone, cells with VC + MMDS are better and cells with VC + DTD and VC + PLS are worse. The trends found here are different from the results obtained using the same additives in graphite/Li[Ni1/3Mn1/3Co1/3]O2 (NMC) pouch cells where cells with VC + DTD and VC + MMDS were found to provide benefit compared to VC alone. It is hard to distinguish any difference between 2% VC and 2%VC + 1% TMS in both graphite/LCO cells and graphite/NMC cells, suggesting that TMS is nearly "inert" in the presence of VC in these cells. [ABSTRACT FROM AUTHOR]

Combinations of vinylene carbonate (VC), a sulfur-containing additive like methylene methane disulfonate (MMDS), and tris(-trimethyl-silyl)-phosphite (TTSPi) and/or tris(-trimethyl-silyl)- phosphate (TTSP) used as electrolyte additives in Li(Ni1/3Mn1/3Co1/3)O2 (NMC111)/graphite Li-ion cells are shown to impart exceptional properties to those cells. These ternary or quaternary additive mixtures: apparently reduce parasitic reactions, such as electrolyte decomposition, at the positive electrode above 4.1 V compared to VC alone; increase the thermal stability of the charged graphite electrode at elevated temperature; improve coulombic efficiency and also reduce impedance of the cells. These factors all suggest longer lived, safer, higher power Li-ion cells with better tolerance to high voltages which will improve energy density. [ABSTRACT FROM AUTHOR]

Vinylene carbonate (VC) and fluoroethylene carbonate (FEC) are compared as electrolyte additives for LiCoO2/graphite pouch cells using the ultra high precision charger (UHPC) at Dalhousie University, an automated storage system, electrochemical impedance spectroscopy (EIS) and long term cycling. Both VC and FEC are useful additives that improve couloumbic efficiency (CE), reduce charge end point capacity slippage, improve long-term cycling and reduce self-discharge during storage compared to cells with control electrolyte. Increasing the concentration of VC over 2% causes a dramatic increase in charge transfer resistance at the negative electrode surface, while the same effect is not observed for FEC. Therefore larger concentrations of FEC can be added to the electrolyte without this problem. However, when 4 or 6% FEC is used, greater gas generation during extended cycling at 40°C is detected. When only a single additive of VC or FEC is used in these LCO/graphite pouch cells tested at 40²C, a concentration of between 2% and 4% VC appears to be optimum as that provides high CE. low charge end point capacity slippage, a small increase in charge-discharge polarization with cycling and a small self discharge during storage. The VC content would be optimized between these limits to trade off lifetime for rate capability. [ABSTRACT FROM AUTHOR]

Wound prismatic LiCoO2/Li4Ti5O12 cells with 1 M LiPF6 in ethylene carbonate (EC):ethyl methyl carbonate (EMC) (3:7 by wt) baseline electrolyte had water intentionally added to the electrolyte and were studied using the High Precision Charger at Dalhousie University, automated cycling/storage, AC impedance and extended cycling. Water was added at 200, 1000 and 2000 ppm to the control electrolyte. The control cells have been shown by the manufacturer to cycle for over four years with only about 1% capacity loss in on-going tests. Swelling during the formation cycle increased gradually when 200 and 1000 ppm water was added and substantially when 2000 ppm water was added. A corresponding increase in first cycle irreversible capacity with increasing water content was observed. Adding up to 2000 ppm water resulted in minimal change to measured coulombic efficiency, charge end point slippage, voltage drop during storage and average charge voltage increase. In fact, most measured parameters were slightly improved with the addition of up to 1000 ppm water compared to control. Measured cell impedance was reduced compared to control cells for all cells containing water. There was no detrimental effect on capacity retention due to the added water for cells tested for 400 charge-discharge cycles. At these relatively low loading levels of water in the electrolyte there were no obvious detrimental effects to cell performance and therefore it may be possible to relax water content specifications in Li-ion battery electrolyte leading to one avenue for cost reduction. [ABSTRACT FROM AUTHOR]

The effects of different concentrations of vinylene carbonate (VC) and vinyl ethylene carbonate (VEC) (0%, 0.5%, 1%, 2%. 4%, and 6% by weight) in LiCoO2/graphite pouch cells in 1M LiPF6 ethylene carbonate (EC): ethyl methyl carbonate (EMC) (3:7 w:w) electrolyte have been studied using high precision coulometry and electrochemical impedance spectroscopy measurements (EIS) on symmetric cells. High precision coulometry showed that when cells were formed at 40'C, VC improves the cycling behavior by reducing the rate of the parasitic reactions at the positive electrode and improving the coulombic efficiency, whereas VEC does not affect the cycling behavior (compared to control). EIS measurements on symmetric cells showed that while VC affects the positive electrode for all concentrations studied and the negative electrode at concentrations higher than 1%. VEC does not affect the negative electrode for all concentrations studied and affects the positive electrode at concentrations higher than 2%. [ABSTRACT FROM AUTHOR]

LNMO/LTO cells represent an excellent vehicle with which to test the impact of electrolyte additives on cell performance due to the high potential of LNMO which leads to electrolyte oxidation. Additives that prevent this oxidation are desired. Electrolyte additive researchers normally compare the capacity retention versus cycle number of cells with and without additives. If the capacity retention is improved, the additive is "good". In this paper, this logic is shown to be flawed. One additive, LiO-t-C4F9, which does improve capacity retention versus cycle number, is shown to do so by increasing electrolyte oxidation at the positive electrode. This causes increased charge end point capacity slippage and increased self discharge rates. As such, these additives, like many promoted in the literature, are not "good", but are "bad". On the other hand, one additive, Al(HFiP)3, is shown to reduce parasitic reactions at the LNMO electrode but does not lead to improved capacity retention. A full understanding of the impact of the additive on the parasitic reaction rates at both positive and negative electrodes is required before a sound judgment about the impact of an additive can be made. Therefore, additive researchers must pay attention to coulombic efficiency, capacity end point slippage, reversible and irreversible capacity loss during storage as well as voltage drop during storage in addition to the long-time cycling performance for cells to get an overall evaluation of electrolyte additives. [ABSTRACT FROM AUTHOR]

A study of LiCoO2/graphite and Li[Ni1/3Co1/3Mn1/3]O2/graphite commercial cells cycling between narrow voltage limits near full state of charge on a high precision charger and stored at various voltages on a custom storage system was performed. It is demonstrated both theoretically and experimentally that narrow range cycling and storage experiments give direct information about the parasitic reactions occurring at the positive electrode in a Li-ion cell. The potential and temperature dependence of these reactions was mapped over the range between 3.95 and 4.2 V and between 30 and 60°C. These techniques should be adopted by researchers and engineers looking to understand the function of electrolyte additives, new electrode materials and electrode material coatings in Li-ion cells. [ABSTRACT FROM AUTHOR]

Wound LiCoO2/graphite cells with 1 M LiPF6 EC:EMC electrolyte containing 1 wt%, 2 wt% vinylene carbonate (VC), 0.3 wt% trimethoxyboroxine (TMOBX) and 2 wt% VC + 0.3 wt% TMOBX were subjected to extended storage studies. After storage, the electrodes were studied using the symmetric cell and electrochemical impedance spectroscopy (EIS) approach described by previous workers. This approach allows the impact of an additive on the impedance of the negative and the positive electrode to be distinguished. Compared to the control cells, adding 1 wt% VC reduced the positive electrode impedance and only slightly affected the negative electrode impedance. Adding 2 wt% VC reduced the positive electrode impedance and greatly increased the negative electrode impedance. An addition of 0.3 wt% TMOBX greatly decreased the positive electrode impedance and slightly increased the negative electrode impedance. Compared to the cells with 2% VC only, adding 2% VC + 0.3% TMOBX decreased the positive electrode impedance without affecting the negative electrode impedance leading to a significant reduction in full cell impedance. These results help explain why the combination of VC and TMOBX additives can be effective in LiCoO2/graphite cells designed for long life time. [ABSTRACT FROM AUTHOR]

Wound LiCoO2/graphite and Li[Ni0.42Mn0.42Co0.16]O2 (NMC)/graphite cells with 1 M LiPF6 in EC:EMC (3:7 by wt) electrolyte containing 2 wt% vinylene carbonate (VC) and/or 0.3 wt% trimethoxyboroxine (TMOBX) were studied using the High Precision Charger at Dalhousie University, automated cycling/storage, AC impedance and long-term cycling at elevated temperature. The additive, VC, improves lifetime performance by increasing coulombic efficiency and decreasing charge and discharge end point capacity slippage. The impact of TMOBX on cell performance depends on electrolyte and electrode choices within the cell. When TMOBX is added to control electrolyte in LiCoO2/graphite cells, the cycle life is improved and the impedance reduced. When added to VC-containing electrolyte the impedance is also reduced with the impact on lifetime not being clear at this time. When TMOBX is added to NMC/graphite cells with control electrolyte the impedance is decreased but when added to VC-containing electrolyte the impedance is unchanged. The impact on cycle life when TMOBX is added to NMC/graphite cells is a decrease in capacity fade but a lower measured coulombic efficiency. Therefore TMOBX appears to be an interesting additive with potential to decrease impedance and/or extend cycle life based on the electrolyte formulation and electrodes used in a Li-ion cell. [ABSTRACT FROM AUTHOR]

Wound LiCoO2/graphite and Li[Ni0.42Mn0.42Co0.16]O2/graphite cells with 1 M LiPF6 in EC:EMC (3:7 by wt) electrolyte containing 2 wt% vinylene carbonate (VC) and/or lithium bis (trifluoromethanesulphonyl) imide (LiTFSI or 3M Fluorad Lithium HQ-115) were studied using the High Precision Charger at Dalhousie University, automated cycling/storage, AC impedance and long-term cycling at elevated temperature. The additive, VC, improves lifetime performance by increasing coulombic efficiency and decreasing charge and discharge end point capacity slippage, while the impact of HQ-115 alone on lifetime is minimal. However, HQ-115 reduces cell impedance when added to either control or VC-containing electrolyte. Therefore it serves as a useful additive for improving the rate capability of cells and capacity retention during high rate cycling at elevated temperature. It is our opinion that Li-ion cells incorporating VC can benefit from a simultaneous addition of HQ-115 due to a synergistic effect observed between HQ-115 and VC additives. This report is the first of two companion reports studying impedance reducing additives and their impact on cell lifetime. [ABSTRACT FROM AUTHOR]

Wound LiCoO2/graphite and Li[Ni0.42Mn0.42Co0.16]O2/graphite cells with 1M LiPF6 EC:EMC electrolyte containing either 0, 1 or 2 wt.% vinylene carbonate were studied using the High Precision Charger at Dalhousie University, automated cell storage and AC impedance. Vinylene carbonate (VC) was found to improve the coulombic efficiency of the cells, decrease charge endpoint capacity slippage and decrease self discharge, in all cases primarily by slowing electrolyte oxidation at the positive electrode. The beneficial impacts of VC are greater in LiCoO2 cells than in Li[Ni0.42Mn0.42Co0.16]O2 cells. One percent VC is enough to derive the benefits without causing an impedance rise in the cells. [ABSTRACT FROM AUTHOR]

Twenty seven LiCoO2/graphite wound prismatic cells containing a variety of electrolyte additives as well as high or low surface area LiCoO2 were studied during high temperature storage using an automated storage system. The same cells had been previously studied using high precision coulometry. Cells were initially cycled to measure the capacity, charged and then stored for one month at either 40 or 60 °C, then cycled again to measure the reversible and irreversible capacity loss. The process was then repeated. During storage, the open circuit potential was automatically measured every 6 hours. The mechanisms responsible for the voltage drop which occurred during storage and the capacity loss after storage were analysed using a Li inventory model. The voltage drop during storage is caused primarily by parasitic reactions (electrolyte oxidation, transition metal dissolution, etc.) that insert Li into the positive electrode, because the potential of the LixC6 electrode is virtually constant on the stage-2/stage-1 plateau even if its Li content changes due to solid electrolyte interface (SEI) growth. The experimental results show that the combination of the electrolyte additive, vinylene carbonate, and low surface area LiCoO2 minimizes the voltage drop and capacity loss during storage presumably by reducing the amount of electrolyte oxidation occurring at the positive electrode. The same cells had charge endpoint capacity slippages that were closest to 0.00%/cycle during cycling tests monitored with high precision coulometry. Storage experiments, in concert with precision coulometry, allow a clear picture of the effect of additives to be determined. [ABSTRACT FROM AUTHOR]