Twenty seven LiCoO 2 /graphite wound prismatic cells containing a variety of electrolyte additives as well as high or low surface area LiCoO 2 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 Li x C 6 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 LiCoO 2 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.Lithium-ion batteries are now being used in electrified vehicles. The cycle and calendar life requirements in vehicular applications are far more demanding than in computer and phone applications. Therefore it is utmost importance to understand cell degradation mechanisms and to use new electrode materials, electrolytes and electrolyte additives to minimize degradation.Capacity loss in Li-ion batteries occurs during storage and cycling. 1-5 There are many possible undesired or parasitic processes, such as dissolution of transition metals from charged positive electrodes, corrosion of current collectors, electrolyte oxidation at the positive electrode, electrolyte reduction at the negative electrode leading to SEI growth, etc. that lead to capacity loss. Capacity retention and storage life of Li-ion cells are critically dependent on the stability of the passivation layers that form on both electrodes. Control of the electrode/electrolyte interfaces is therefore key to obtain Li-ion cells with long lifetimes.It was suggested by Broussely et al. 2 that lithium consumption at the negative electrode affected cell capacity during storage at high temperature. They also concluded that electrolyte oxidation at the positive electrode resulted in additional losses during storage at high voltage.Electrolyte additives, such as vinylene carbonate (VC), are known to improve cycl...

LiCoO 2 /graphite and LiCoO 2 /Li 4 Ti 5 O 12 wound prismatic cells were examined with and without electrolyte additives using the high precision charger at Dalhousie University. The additives tested were vinylene carbonate, trimethoxyboroxine, and lithium ͑bis͒ trifluoromethanesulfonimide. The voltage curves, charge and discharge end point positions, fade, and coulombic efficiency were compared to gain an understanding of the effects of the electrolyte additives on the cells. Long term cycling data ͑capacity loss over 750 cycles͒ was compared with predicted lifetime measurements based on high precision coulometry. Design of experiments was used in order to help interpret the results from the 20 groups of cells tested.Lithium-ion batteries ͑LIBs͒ used in electrified vehicles and for grid energy applications require larger capacities, longer cycle life, and longer calendar life than previously required in portable electronics ͑e.g., laptops and cell phone͒ applications. Electrolyte additives have been extensively studied and are used to improve the lifetime of LIBs. [1][2][3][4][5][6][7][8] One of the most commonly used electrolyte additives is vinylene carbonate ͑VC͒. 2-5 Aurbach et al. 2 studied the impact of VC and found that its reduction at a graphite negative electrode takes place before the reduction of ethylene carbonate, which forms a flexible and cohesive polymeric surface species that acts as a more stable solid electrolyte interface ͑SEI͒. The authors also believed that this type of unique surface reaction may be occurring on the positive electrode, stabilizing its SEI as well. Ota et al. 3 examined the improved SEI formed on graphite with the addition of VC. Another paper from the same group showed the beneficial impact of VC at higher temperature and attributed it to increased Li + ion mobility and stated that the addition of VC has a large impact on the negative electrode but could benefit the positive electrode as well. 4 Other less studied additives include trimethoxyboroxine ͑TMOBX͒ and LiN͑CF 3 SO 2 ͒ 2 ͑called HQ-115 here͒. TMOBX is made of a ͑BO͒ 3 ring with methyl groups attached to the boron atoms. Mao et al. 6 showed that the presence of ͑BO͒ 3 rings dissolved in electrolyte reduced the capacity loss during cycling of 18,650-size cells ͑LiCoO 2 /graphite and LiMn 2 O 4 /graphite͒ and that the additive with the methyl groups attached to the ring proved more effective. Small concentrations ͑Ͻ 1%͒ were added to see this benefit. 6 HQ-115 is a Li-salt ideal for organic electrolyte-based lithium batteries. HQ-115 has better thermal stability than LiPF 6 resulting from the strong covalent bonding nature of the negative ion. 7,8 It is believed by the authors that HQ-115 is used as an electrolyte additive in prismatic and pouch-type Li-ion cells to limit gas generation during operation.A major problem for researchers is the inability to conveniently determine the cycle life and calendar life of lithium-ion batteries under actual duty cycles that will be used in the field. For example, a pure elect...

Scanning electrochemical microscopy (SECM) is used to map localized iontophoretic fluxes of electroactive species through porous membranes. A method is described that allows both the rate of transport of species from a microscopic pore and the pore's diameter to be measured. SECM images and analyses of synthetic porous membranes (track-etched polycarbonate and mica membranes) and hairless mouse skin are reported. Preliminary analysis of SECM images of the mouse skin indicates that a significant percentage of the iontophoretic flux occurs through pores associated with hair follicles.

A method of determining absolute rates of diffusion and electroosmotic convective flow through individual pores in porous ion-selective membranes is described. The method is based on positioning a scanning electrochemical microscope (SECM) tip directly above a membrane pore and detecting electroactive molecules as they emerge from the pore. Absolute diffusive and electroosmotic fluxes, electroosmotic drag coefficient, convective velocity, and pore radius can be evaluated in a single experiment by measuring the faradaic current at the SECM tip as a function of the iontophoretic current passed across the membrane. Electroosmotic transport of hydroquinone through a permselective polymer (Nafion), contained within ∼50-µm-radius pores of a 200-µm-thick mica membrane, is used as a model system to demonstrate the analytical method. Analysis of electroosmotic transport parameters obtained by SECM suggests that the average electroosmotic velocities of solvent (H 2 O) and solute (hydroquinone) in the Nafion are significantly different, a consequence of the differences in their chemical interactions with the current-carrying mobile cations (Na + ).Iontophoresis is the transport of molecular species under the influence of an electrical potential gradient. 1 The pharmaceutical and medical communities are actively researching the iontophoretic transport of ions and molecules through skin as an alternative method of drug administration for humans. 2 In this application, a small electrical current is driven between two electrodes that are placed in contact with the outer surface of the skin. The molecular species of interestsi.e., the drugsis dissolved in a thin layer of solution between one electrode and the skin and is transported across the skin at a continuously controlled rate that is determined by the applied current. The drug molecules traverse the skin and are transported throughout the body by the circulatory system.

Wound LiCoO 2 /graphite and Li[Ni 0.42 Mn 0.42 Co 0.16 ]O 2 /graphite cells with 1M LiPF 6 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 LiCoO 2 cells than in Li[Ni 0.42 Mn 0.42 Co 0.16 ]O 2 cells. One percent VC is enough to derive the benefits without causing an impedance rise in the cells.