Galvanostatic Intermittent Titration Technique Reinvented: Part II. Experiments

Following a critical review of the galvanostatic intermittent titration technique in Part I, here we experimentally demonstrate how to extract chemical diffusivity with a modified method. We prepare dense bulk samples that ensure diffusion-limitation. We utilize the scaling with t relax + τ − t relax (t relax: relaxation time; τ: pulse duration), avoiding problems with composition-dependent overpotentials. The equilibrium Nernst voltage is measured separately using small porous particles. This separation between the diffusion measurement and the titration procedure is critical for performing each measurement in a reliable setting. We report the chemical diffusion coefficients of LixNi1/3Mn1/3Co1/3O2 and their activation energy. We extract ionic conductivity and compare it with total conductivity to confirm ion-limitation in chemical diffusion. The measurements suggest that the time scale for diffusion in typical Li-ion battery particles could be much shorter than that of the intercalation/deintercalation processes at the particle surface (Biot number less than 0.1).

Galvanostatic Intermittent Titration Technique Reinvented: Part I. A Critical Review

The galvanostatic intermittent titration technique (GITT), introduced in 1977 by Weppner and Huggins, provided a readily accessible means to measuring the chemical diffusion coefficient of electrochemical electrode materials. The method continues to be widely used today, but the reported diffusivity values are highly inconsistent, ranging as much as four orders of magnitude for some Li layered oxide compositions. Even qualitative trends of diffusivity are inconsistent, suggesting significant flaws in the implementation of the method. Other variants of the GITT method also suffer from similar inconsistency problems. Here we identify numerous sources of significant error including composition-dependent reaction overpotentials, mathematical flaws in the relaxation analysis methods, finite-size and non-planar geometry effects, inter-particle inhomogeneity issues, early transient effects, and surface area uncertainties. We propose a simple relaxation analysis scheme using the time variable t relax + τ − t relax , where t relax is relaxation time and τ is the galvanostatic pulse duration. We also propose to use dense diffusion-limited samples to isolate the bulk-diffusion process in the time domain. Chemical diffusivity can be extracted much more reliably with this improved implementation of the GITT method.

Study on Adaptive Cycle Life Extension Method of Li-Ion Battery Based on Differential Thermal Voltammetry Parameter Decoupling

Battery aging leads to reduction in a battery’s cycle life, which restricts the development of energy storage technology. At present, the state of health (SOH) assessment technology, which is used to indicate the battery cycle life, has been widely studied. This paper tries to find a way to adjust the battery management system adaptively in order to prolong the battery cycle life with the change of SOH. In this paper, an improved Galvanostatic Intermittent Titration Technique (GITT) method is proposed to decouple the terminal voltage into overpotential (induced by total internal resistance) and stoichiometric drift (caused by battery aging, indicated by OCV). Based on improved GITT, the open circuit voltage-temperature change (OCV-dT/dV) characteristics of SOH are described more accurately. With such an accurate description of SOH change, the adaptive method to change the discharge and charge cut-off voltage is obtained, whose application can prolong battery cycle life. Experiments verify that, in the middle of a battery’s life-cycle, the adaptive method to change the discharge and charge cut-off voltage can effectively improve the cycle life of the battery. This method can be applied during the period of preventive maintenance in battery storage systems.

Kinetics of electrochemical intercalation of lithium ion into Li[Li0.2Co0.3Mn0.5]O2 electrode from Li2SO4 solution

The kinetics of electrochemical lithium ion intercalation into Li[Li0.2Co0.3Mn0.5]O2 electrode in 2 M Li2SO4 aqueous electrolyte has been studied using two electroanalytical methods, namely, potentiostatic intermittent titration technique (PITT) and galvanostatic intermittent titration technique (GITT). The results are compared with those from nonaqueous electrolytes. Layered, lithium-rich Li[Li0.2Co0.3Mn0.5]O2 cathode material was synthesized by reactions under autogenic pressure at elevated temperature (RAPET) method. The effects of ohmic potential drop and charge-transfer resistance have been considered while predicting the current transients obtained with aqueous electrolyte. For PITT and GITT, we have defined their characteristic time-invariant functions, It1/2 and dE/dt1/2, respectively to present the diffusion time constant τ. Application of different theoretical diffusion models for treating the results obtained by the above-mentioned techniques allowed us to calculate the diffusion coefficient of lithium ions (D) at different potentials (E). The intercalation process is explained by considering the possible attractive interactions of the intercalated species in terms of Frumkin intercalation isotherm. We have observed a strictcorrespondence between the peaks of the intercalation capacitance and the minima in the corresponding log D vs. E curve.

In vitro carminative and in vivo antidiarrheal activity of Citrus maxima

In this study, the methanolic extracts of leaves of Citrus maxima were evaluated for their carminative and antidiarrheal activities. By soxhlet method, the methanolic extract of leaves of Citrus maxima was prepared. Carminative activity of methanolic extract was studied in vitro by acid-base titration technique and antidiarrheal activity was studied in rats by castor oil induced diarrhoea method. The phytochemical screening was done using various chemical tests. Alkaloids, tannins, carbohydrates, flavonoids, terpenoids, amino acids, anthraquinones, glycosides are confirmed to be present in the leaf. Carminative activity of extract was found significantly less with 5mL, when compared with 10mL extract. The antidiarrheal activity observed in the animals treated with 200mg/kg showed significant activity compared with the animals treated with 100mg/kg. The study revealed that carminative activity and antidiarrheal activity of methanolic extract of C. maxima. May be the extract acts on circular and longitudinal intestinal muscle by inhibiting acetylcholine and prostaglandins, which reduces peristaltic movements and prolongs transmit time, reduces fecal volume, increases viscosity and viscous fluid and electrolyte loss. The compound in the extract causes mild irritation resulting in vasodilation of gastrointestinal muscles, thereby relieving cramping and expels gas

Investigation of Lithium Ion Diffusion of Graphite Anode by the Galvanostatic Intermittent Titration Technique

Graphite is used as a state-of-the-art anode in commercial lithium-ion batteries (LIBs) due to its highly reversible lithium-ion storage capability and low electrode potential. However, graphite anodes exhibit sluggish diffusion kinetics for lithium-ion intercalation/deintercalation, thus limiting the rate capability of commercial LIBs. In order to determine the lithium-ion diffusion coefficient of commercial graphite anodes, we employed a galvanostatic intermittent titration technique (GITT) to quantify the quasi-equilibrium open circuit potential and diffusion coefficient as a function of lithium-ion concentration and potential for a commercial graphite electrode. Three plateaus are observed in the quasi-equilibrium open circuit potential curves, which are indicative of a mixed phase upon lithium-ion intercalation/deintercalation. The obtained diffusion coefficients tend to increase with increasing lithium concentration and exhibit an insignificant difference between charge and discharge conditions. This study reveals that the diffusion coefficient of graphite obtained with the GITT (1 × 10−11 cm2/s to 4 × 10−10 cm2/s) is in reasonable agreement with literature values obtained from electrochemical impedance spectroscopy. The GITT is comparatively simple and direct and therefore enables systematic measurements of ion intercalation/deintercalation diffusion coefficients for secondary ion battery materials.

Hydrothermally synthesized nanostructured LiMnxFe1−xPO4 (x = 0–0.3) cathode materials with enhanced properties for lithium-ion batteries

Nanostructured cathode materials based on Mn-doped olivine LiMnxFe1−xPO4 (x = 0, 0.1, 0.2, and 0.3) were successfully synthesized via a hydrothermal route. The field-emission scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyzed results indicated that the synthesized LiMnxFe1−xPO4 (x = 0, 0.1, 0.2, and 0.3) samples possessed a sphere-like nanostructure and a relatively homogeneous size distribution in the range of 100–200 nm. Electrochemical experiments and analysis showed that the Mn doping increased the redox potential and boosted the capacity. While the undoped olivine (LiFePO4) had a capacity of 169 mAh g−1 with a slight reduction (10%) in the initial capacity after 50 cycles (150 mAh g−1), the Mn-doped olivine samples (LiMnxFe1−xPO4) demonstrated reliable cycling tests with negligible capacity loss, reaching 151, 147, and 157 mAh g−1 for x = 0.1, 0.2, and 0.3, respectively. The results from electrochemical impedance spectroscopy (EIS) accompanied by the galvanostatic intermittent titration technique (GITT) have resulted that the Mn substitution for Fe promoted the charge transfer process and hence the rapid Li transport. These findings indicate that the LiMnxFe1−xPO4 nanostructures are promising cathode materials for lithium ion battery applications.