Discharge Capacity Of Cell Research Articles

Optimal charge rates for a lithium ion cell

The optimum charge rate for a lithium ion cell at each cycle is determined to maximize the useful life of the cell without using optimization algorithms. In previous work, we showed that by applying a dynamic optimization routine the number of cycles can be increased by approximately 29.4% with respect to the case with one optimal charge current [7]. The dynamic optimization results indicated that the optimum charge rates are the minimum currents at which the constraints for the useful life are satisfied. This is due to the minimum charge rate resulting in minimum side reaction rate and capacity fade. Useful cell life is defined as the number of cycles before the end of discharge voltage (EODV) drops below 3.0 V or the cell discharge capacity becomes less than 20% of the original discharge capacity. The new approach presented in this work is able to find the optimal charge rates in a few minutes while the previous optimization algorithm takes at least one day, and improves the useful cell life by approximately 41.6% with respect to using only one optimal charge current.

New insights into the limiting parameters of the Li/S rechargeable cell

The lithium/sulfur (Li/S) battery is a promising electrochemical system that has high theoretical capacity of 1675 mAh g −1. However, the system suffers from several drawbacks: poor active material conductivity, active material dissolution, and use of the highly reactive lithium metal electrode. This study was aimed at understanding the most important limiting parameters of a Li/S cell. Different sulfur material pre-treatments were experimented to increase the practical capacity, and various morphologies were obtained. But none of these treatments led to improvements in electrochemical performance. Electrolyte additives were also used to increase cell discharge capacity, but again without success. Finally, it was concluded that the cell capacity limitation may be linked to dissolution of sulfur material and to passivation of the positive electrode. As the final discharge products are insulating and poorly soluble, they precipitate and induce passivation of the positive electrode surface, leading to incomplete active material utilization. EIS measurements confirmed this passivation problem.

SiO2/styrene butadiene rubber-coated poly(ethylene terephthalate) nonwoven composite separators for safer lithium-ion batteries

We develop a new nonwoven composite separator for a safer lithium-ion battery, which is based on coating of silica () colloidal particles/styrene-butadiene rubber (SBR) binder to a poly(ethylene terephthalate) (PET) nonwoven support. The particles are interconnected by the SBR binder and closely packed in the nonwoven composite separator, which thus allows for the development of unusual porous structure, i.e. highly-connected interstitial voids formed between the particles. The PET nonwoven serves as a mechanical support that contributes to suppressing thermal shrinkage of the nonwoven composite separator. The /SBR content in the nonwoven composite separators plays an important role in determining their separator properties. Porous structure, air permeability, and electrolyte wettability of the nonwoven composite separators, in comparison to a commercialized polyethylene (PE) separator, are elucidated as a function of the /SBR content. Based on this understanding of the nonwoven composite separators, the effect of /SBR content on the electrochemical performances such as self-discharge, discharge capacity, and discharge C-rate capability of cells assembled with the nonwoven composite separators is investigated.

Maximizing the Life of a Lithium-Ion Cell by Optimization of Charging Rates

Using a dynamic optimization method, the optimum charge currents as a function of cycle number during cycling for the lithium-ion cell are obtained. A single particle physics-based model, which includes capacity fade, was applied to simulate the cell performance under low earth-orbit (LEO) cycling conditions. Useful cell life is defined as the number of cycles before the end of discharge voltage drops below 3.0 V or the cell discharge capacity becomes less than 20% of the original discharge capacity. The simulated useful cell life can be increased by by varying the charge current.

Direct write dispenser printing of a zinc microbattery with an ionic liquid gel electrolyte

The need for energy dense microbatteries with miniature dimensions has prompted the development of unconventional materials, cell geometries, and processing methods. This work will highlight our materials investigations, deposition methods and the device performance of a printed zinc–manganese dioxide rechargeable microbattery utilizing an ionic liquid gel electrolyte. We have developed a direct write dispenser printing method with the ability to fabricate multilayer structures and precisely deposit and pattern these components onto any substrates. The use of a unique room-temperature ionic liquid swelled into a polymer to form a gel electrolyte with solid-like mechanical strength and liquid-like ion transport properties has enabled the simple fabrication of stacked microbattery structures with the potential to be easily integrated directly onto a microdevice substrate. Initial microbattery tests and cycle behavior are discussed, and after an initial activation of the cathode material, an experimental cell discharge capacity and energy density of 0.98 mA h cm−2 and 1.2 mW h cm−2 were measured, respectively.

LiPF 6 and lithium oxalyldifluoroborate blend salts electrolyte for LiFePO 4/artificial graphite lithium-ion cells

The electrochemical behaviors of LiPF 6 and lithium oxalyldifluoroborate (LiODFB) blend salts in ethylene carbonate + propylene carbonate + dimethyl carbonate (EC + PC + DMC, 1:1:3, v/v/v) for LiFePO 4/artificial graphite (AG) lithium-ion cells have been investigated in this work. It is demonstrated by conductivity test that LiPF 6 and LiODFB blend salts electrolytes have superior conductivity to pure LiODFB-based electrolyte. The results show that the performances of LiFePO 4/Li half cells with LiPF 6 and LiODFB blend salts electrolytes are inferior to pure LiPF 6-based electrolyte, the capacity and cycling efficiency of Li/AG half cells are distinctly improved by blend salts electrolytes, and the optimum LiODFB/LiPF 6 molar ratio is around 4:1. A reduction peak is observed around 1.5 V in LiODFB containing electrolyte systems by means of CV tests for Li/AG cells. Excellent capacity and cycling performance are obtained on LiFePO 4/AG 063048-type cells tests with blend salts electrolytes. A plateau near 1.7–2.0 V is shown in electrolytes containing LiODFB salt, and extends with increasing LiODFB concentration in charge curve of LiFePO 4/AG cells. At 1 C discharge current rate, the initial discharge capacity of 063048-type cell with the optimum electrolyte is 376.0 mAh, and the capacity retention is 90.8% after 100 cycles at 25 °C. When at 65 °C, the capacity and capacity retention after 100 cycles are 351.3 mAh and 88.7%, respectively. The performances of LiFePO 4/AG cells are remarkably improved by blending LiODFB and LiPF 6 salts compared to those of pure LiPF 6-based electrolyte system, especially at elevated temperature to 65 °C.

Relative Impact of Al or Mg Substitution on the Thermal Stability of LiCo1 − zMzO2 (M = Al or Mg) by Accelerating Rate Calorimetry

Al- or Mg-substituted ( or Mg) samples were synthesized by a coprecipitation-based method followed by heating with at for and again at for . Electrochemical studies showed that Al or Mg substitution reduces the initial discharge capacity of cells but does not strongly impact their cycle life. The effects of Al or Mg substitution on the thermal stability of charged were studied by accelerating rate calorimetry and indicate that Al substitution is far more effective than Mg substitution in improving the thermal stability of .

Pulsed-Laser-Deposited Sn4P3 Electrodes for Lithium-Ion Batteries

thin films have been successfully fabricated by reactive pulsed laser deposition for the first time and were investigated for their electrochemistry with lithium. The reversible discharge capacity of cells cycled between 0 and was found to be about . By using ex situ X-ray diffraction, transmission electron microscopy, and selected-area electron diffraction measurements, both the classical alloying process and the phosphorization∕reduction of nanosized Sn were revealed in the lithium electrochemical reaction of film electrode. Large reversible capacity of made it a potential anode material for future lithium-ion batteries.

Polyvinylidene fluoride membrane by novel electrospinning system for separator of Li-ion batteries

The remarkable characteristics of nanofibers mats electrospun are large surface area to volume ratio and high porosity, which are crucial to increase the ionic conductivity of membrane full of liquid electrolyte, in this aspect, electrospinning is prior to the other methods, such as dry method, wet method, etc. Therefore, fabricating the separator of Li-ion batteries by electrospinning is potential and promising. The PVDF membranes were fabricated by electrospinning. The experiment demonstrated that the main deficiency in the fabricating separators process by electrospinning was low mechanical property, which induced partial short circuits inside the cells. Several methods were presented to enhance the mechanical strength. The experiments demonstrated that the higher the solution concentration was, the stronger the mechanical strength was, and the higher the voltage was, the stronger the mechanical strength was. Additionally, the spherical hat collection target instead of conditional plane target was applied in the electrospinning system, as a result, the thickness of the membrane was more uniform and the fiber diameter was also more uniform. Therefore, the charge and discharge capacity of the coin type cell composed of the separator collected by spherical hat target exceeded the plane target, and the electrospinning separators exceeded the commercial polypropylene separator.

Diphenyloctyl phosphate and tris(2,2,2-trifluoroethyl) phosphite as flame-retardant additives for Li-ion cell electrolytes at elevated temperature

The effect of diphenyloctyl phosphate (DPOF) and tris(2,2,2-trifluoroethyl) phosphite (TTFP) as flame-retardant (FR) additives in the liquid electrolyte of Li-ion cells is evaluated at both elevated temperature (40 °C) and room temperature (RT, 25 °C). The tested cells use mesocarbon microbeads (MCMB) and LiCoO 2 as the anode and cathode materials, respectively. Cell characteristics are investigated by means of electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The results of the cycle performance tests demonstrate the superior discharge capacity and capacity retention of the DPOF-containing cell compared will TTFP after cycling at both RT and 40 °C. Therefore, these results confirm the promising potential of DPOF as an FR additive for improving the electrochemical performance of Li-ion batteries.

Relation between composition of the positive electrode and cell performance and safety of lithium-ion PTC batteries

To improve the safety of lithium-ion batteries, a new type of positive electrode, which contains a positive temperature coefficient (PTC) compound consisting of a carbon black/polyethylene composite as the conductive material, was fabricated. The relation between the positive electrode composition and both the discharge characteristics and safety was investigated. The discharge capacity of PTC cells increased as the PTC compound ratio decreased or the acetylene black (AB) ratio increased. In an external short-circuit test, the maximum short-circuit current decreased with an increase in the PTC compound ratio, or with a decrease in the AB ratio. Moreover, in an overcharge test, the voltage of the PTC cells with any composition increased earlier than that in a conventional cell and a cell with a high PTC compound ratio showed high overcharge tolerance. Based on the results of X-ray diffraction (XRD) measurements for the positive electrodes of PTC cells, it was clear that there was inadequate oxidation of the active material, since the Li + extraction reaction from Li x CoO 2 hardly progress at the part of the active material which contacts the PTC compound due to an increase in the resistance of the PTC compound at the high temperature.

Electrochemical properties of lithium sulfur cells using PEO polymer electrolytes prepared under three different mixing conditions

Lithium sulfur cells were prepared by composing with sulfur cathode (PEO) 6LiBF 4 polymer electrolyte and lithium anode. (PEO) 6LiBF 4 polymer electrolyte was prepared under three different mixing conditions: stirred polymer electrolyte (SPE), ball-milled polymer electrolyte (BPE) and ball-milled polymer electrolyte with 10 wt%Al 2O 3 (BCPE). The effects of ball milling and additive were investigated by discharge test according to depth of discharge. The initial discharge capacity of lithium sulfur cell using BCPE was 1670 mAh g −1-sulfur, which was better than those of SPE and BPE, and approximately equal to the theoretical capacity. The cycle performance of Li/(PEO) 6LiBF 4/S cell was remarkably improved by the addition of Al 2O 3.

Electrochemical Properties of Al Doped Li(Ni<sub>1/3</sub>Co<sub>1/3</sub>Mn<sub>1/3</sub>)O<sub>2</sub>

Al doped Li(Ni1/3Co1/3Mn1/3-xAlx)O2 (x=0.005, 0.01, 0.05) and Li(Ni1/3-x/2Co1/3Mn1/3-x/2Alx)O2 (x=0.01, 0.05) cathode materials for lithium ion batteries were synthesized using an ultrasonic spray pyrolysis and heat treatment. The substitution with Al reduced the content of Mn3+, promoted grain growth, and broadened the particle size distribution of synthesized powders. The initial discharge capacity of cells made with 0.5 mol% Al doped Li(Ni1/3Co1/3Mn1/3-0.005Al0.005)O2 powder was as high as that of the undoped (~180 mAhg-1, 3.04.5 V), and showed an excellent cycle stability. The improvement of the cycle stability was considered to be due to the decrease of Mn3+ in Li(Co1/3Ni1/3Mn1/3-xAlx)O2 by Al doping.

Effect of the dispersity of components of a cathode mixture on discharge characteristics of a Leclanché cell

The effect of dispersity of electrolytic manganese dioxide and of an electrically conducting additive to the cathode mixture on the discharge capacity of chemical power cells of the manganese-zinc system with a salt electrolyte was studied.

Effects of Multiwalled Carbon Nanotubes on the Cycle Performance of Sulfur Electrode for Li/S Secondary Battery

Lithium sulfur cells were prepared by composing with sulfur cathode, 0.5M LiCF3SO3 in tetra ethylene glycol dimethyl ether (TEGDME) solution and lithium anode. Multiwalled carbon nanotubes (MWNTs) were used to form the high electric network and prevent the dissolution of lithium polysulfides in sulfur cathode. The effects of additive contents were investigated by discharge test. The morphology of cathode with MWNTs (20wt.%) has rough and submicro porous. The initial discharge capacity of lithium sulfur cell using multiwalled carbon nanotubes (MWNTs) was 1,200mAh/g-sulfur, which was better than those of acetylene black (AB). The cycle performance of lithium sulfur cell was remarkably improved by the the addition of MWNTs.

Development of new safe electrode for lithium rechargeable battery

A new concept cathode was proposed to improve the safety of lithium rechargeable batteries. The cathode contains a positive temperature coefficient (PTC) compound that can drastically increase resistivity at more than a specified temperature (PTC properties). A PTC cathode containing the PTC compound was fabricated and its resistivity was evaluated. The resistivity of PTC cathodes increased by several tens at 130–140 °C, which is the melting point of polyethylene. In lithium rechargeable batteries using these cathodes (PTC cell), a level nearly reaching the designed capacity is obtained at less than 1 C rate. The discharge capacity of PTC cells became high as the content of PTC compound increases. Moreover, under 3 C discharge condition, the voltage of PTC cell dropped at 138 °C where the resistivity of the PTC cathode drastically increased. Additionally, on the external short circuit test at 145 °C, the short circuit current of the PTC cell was almost 0 A. These results indicate that PTC cathodes will improve the battery safety.

Effects of ultrasound on lithium metal rechargeable battery characteristics at high charging rate

In this work, ultrasound was imposed on Li metal anode to investigate its effects on lithium battery characteristics at high-rate charging process. It was found that under sonicated condition there was higher exchange current density ( I 0) of Li metal, that could effectively decrease the cathodic overpotential of lithium electrode. Meanwhile, lower interfacial impedance of Li anode during high-rate charging process was revealed, if ultrasound imposed. Consequentially, with the depolarization effect of ultrasound on Li anode at high-rate charging process, higher charge and discharge capacity of lithium cell was obtained.

리튬이온폴리머전지용 가교형 겔폴리머전해질의 중합조건 최적화 연구

In this work, polymerization conditions of the gel polymer electrolyte (GPE) were studied to obtain better electrochemical performances in a lithium-ion polymer battery. When the polymerization temperature and time of the GPE were 70 and 70 min, respectively, the lithium polymer battery showed excellent a rate capability and cycleability. The TMPETA (trimethylolpropane ethoxylate triacrylate)/TEGDMA (triethylene glycol dimethacrylate)-based cells prepared under optimized polymerization conditions showed excellent rate capability and low-temperature performances: The discharge capacity of cells at 2 Crate showed 92.1 % against 0.2C rate. The cell at -20 also delivered 82.4 % of the discharge capacity at room temperature.

On the discharge capability and its limiting factors of commercial 18650 Li-ion cell at low temperatures

We here study the discharge capability of commercial 18650 cylindrical lithium-ion cells at low temperatures. The discharge capacity at −20 °C ranges from 67 to 88% of the rated capacity at 0.2 C rate, which is good. However, the cell discharge capacity varies substantially at −30 and −40 °C among the studied cells. It ranges from 2 to 70% of the rated capacity at −30 °C, and 0 to 30% at −40 °C at 0.2 C rate. The cell impedance at 1 kHz increases very little from room temperature down to −20 or −30 °C in general, which does not correlate with the cell discharge capability. However, the dc impedance is increased by a factor of about ten at −30 °C and about twenty at −40 °C from room temperature. The discharge capability at low temperature correlates well with the dc resistance at both room and low temperatures. The limiting factors in the discharge capability at low temperatures and the direction for the future improvement are discussed according to the cell discharge capability, the electrode geometric area, the cell impedance at 1 kHz, and the dc impedance at various temperatures. It appears that the ionic conductivity of the electrolyte and lithium solid diffusion in the electrode do not limit the cell discharge capability, while the lithium diffusion in the SEI layer on the positive surface may be the limiting factor. Cell discharge capability at low temperature does not correlate with cycle life at room temperature.

Behavior of interfacial resistance at lithium electrode for gel electrolyte using novel three-dimensional network polymer host

Abstract A novel macromonomer based on tri-functional poly (alkylene oxide) main chain with acrylate chain ends was specially designed and synthesized for gel electrolyte purpose. Various kinds of gel electrolyte, based on the crosslinked macromonomer, were prepared. Interfacial resistance between lithium electrodes and the gel electrolytes was measured. The significant decrease in interfacial resistance was observed during 4–6 h after assembling the cell. The discharge capacity of secondary cells with the gel electrolyte depended on the kind of liquid electrolyte incorporated in the gel electrolyte.