Open Circuit Voltage Curve Research Articles

Property Evolution of Al2O3 Coated and Uncoated Si Electrodes: A First Principles Investigation

In order to compare the difference between coated and uncoated Si electrode, the basic material properties of atomic layer deposition ALD-Al2O3 coating and native SiO2 layer on Si are investigated by using density functional theory calculations. These properties include: the open circuit voltage curve with respect to lithium metal, the elastic properties, and Li ion diffusion characteristics in SiO2 and Al2O3 and their lithiated compounds (such as Li4SiO4 and LiAlO2). Results show that lithiation occurs at the voltage above EC (Ethylene Carbonate) decomposition(∼0.8V) causing initial irreversible capacity loss. Also, lithiation softens Al2O3 mechanically, while slightly stiffens SiO2. For the Li ion diffusion, SiO2 and Al2O3 have totally different behavior upon lithiation. For SiO2, Li diffuses very fast, but the energy barrier becomes higher as lithiation goes on. When SiO2 is lithiated to Li4SiO4, the diffusion energy barrier becomes lower again. For Al2O3, its intrinsic ionic conductivity is very low, but the Li diffusion energy barrier becomes lower (as low as Li2Si2O5) as lithiation proceeds and LiAlO2 is formed. Therefore, designing ALD coating should target the coating properties after lithiation.

Advancements in OCV Measurement and Analysis for Lithium-Ion Batteries

Incremental open-circuit voltage (OCV) curves and low-current charge/discharge voltage profiles of a lithium-ion (Li-ion) battery are compared and evaluated for optimizing measurement time and resolution. Since these curves are often used for further analysis, minimizing kinetic contributions is crucial for approximating battery OCV behavior. In this context, an incremental OCV measurement is characterized by state of charge (SOC) intervals and relaxation times. Various constant low C-rates, SOC intervals, and relaxation times are tested for approximating OCV behavior. Differential capacity and voltage analysis is used to check whether the main electrode features can be resolved satisfactorily. An interpolation method yields additional data points for the differential analysis of incremental OCV curves. It is shown that incremental OCV measurements are suitable for an approximation of battery OCV behavior, rather than low current-voltage profiles. Furthermore, extrapolation of voltage relaxation enables the estimation of fully relaxed OCV.

A robust state-of-charge estimator for multiple types of lithium-ion batteries using adaptive extended Kalman filter

This paper presents a novel data-driven based approach for the estimation of the state of charge (SoC) of multiple types of lithium ion battery (LiB) cells with adaptive extended Kalman filter (AEKF). A modified second-order RC network based battery model is employed for the state estimation. Based on the battery model and experimental data, the SoC variation per mV voltage for different types of battery chemistry is analyzed and the parameters are identified. The AEKF algorithm is then employed to achieve accurate data-driven based SoC estimation, and the multi-parameter, closed loop feedback system is used to achieve robustness. The accuracy and convergence of the proposed approach is analyzed for different types of LiB cells, including convergence behavior of the model with a large initial SoC error. The results show that the proposed approach has good accuracy for different types of LiB cells, especially for C/LFP LiB cell that has a flat open circuit voltage (OCV) curve. The experimental results show good agreement with the estimation results with maximum error being less than 3%.

Cell state-of-charge inconsistency estimation for LiFePO4 battery pack in hybrid electric vehicles using mean-difference model

Identification of cell SOC (state-of-charge) inconsistency for LiFePO4 battery packs is challenging due to the demanding conditions in hybrid electric vehicles (HEVs) and the relatively flat SOC–OCV (open circuit voltage) curve of LiFePO4 cells compared to others. We experimentally investigate cell voltages in a small battery pack and propose a Mean-plus-Difference Model (M+D Model). The M+D Model uses a cell mean model (CMM) representing the overall performance of the pack in high frequency. Meanwhile cell voltage differences (CVDs) between cells and the “mean cell” are studied by a cell difference model (CDM) in low frequency. A CDM considering SOC and internal resistance differences is subsequently presented and OCV differences are estimated. We further propose an SOC strategy to accurately identify cell SOC inconsistency by intermittently lowering pack SOC to 30% during HEV operation. Finally we discover that SOC differences can be determined with estimated OCV differences using SOC-difference/OCV-difference curve. The proposed method is verified by simulation and experiment. With the proposed method, LiFePO4 cell SOC inconsistency can be precisely estimated with existing measuring technology during HEV operating and cell equalization can be ultimately implemented.

On-board state of health monitoring of lithium-ion batteries using incremental capacity analysis with support vector regression

Battery state of health (SOH) monitoring has become a crucial challenge in hybrid electric vehicles (HEVs) and all electric vehicles (EVs) research, as SOH significantly affects the overall vehicle performance and life cycle. In this paper, we focus on the identification of Li-ion battery capacity fading, as the loss of capacity and therefore the driving range is a primary concern for EV and plug-in HEV (PHEV). While most studies on battery capacity fading are based on laboratory measurement such as open circuit voltage (OCV) curve, few publications have focused on capacity loss monitoring during on-board operations. We propose a battery SOH monitoring scheme based on partially charging data. Through analysis of battery aging cycle data, a robust signature associated with battery aging is identified through incremental capacity analysis (ICA). Several algorithms to extract this signature are developed and evaluated for on-board SOH monitoring. The use of support vector regression (SVR) is shown to provide the most consistent identification results with moderate computational load. For battery cells tested, we show that the SVR model built upon the data from one single cell is able to predict the capacity fading of 7 other cells within 1% error bound.

In-Situ Measurement of Current Distribution in a Li-Ion Cell

This paper reports in-situ measurements of current distribution in a Li-ion battery using a newly developed pouch cell with a segmented electrode. It is shown that current distribution is non-uniform from the beginning of discharge and evolves dramatically as discharge proceeds. Initially, segments closer to the negative tab generate higher local currents, which is attributed to the ohmic potential drop along the negative current collector. However, toward the end of discharge the current distribution reverses in pattern due to local SOC non-uniformity developed by uneven current production in early stages. Current distribution is more uniform at lower C rates and lower temperatures. In cells operated close to the equilibrium (e.g. at low C-rates or higher temperatures), current distribution tends to be wavy as it is dominated by the SOC non-uniformity effect and reflective of multiple plateaus in the open-circuit voltage vs. SOC curve. In contrast, current distribution exhibits a monotonic variation in cells operated at highly non-equilibrium as the ohmic potential drop along the current collector becomes more controlling. Local SOC distribution is calculated based on measured local currents. The SOC distribution is found not uniform, even at cutoff during high C rate discharge, suggesting strongly under-utilization of active materials.

A comparative study of state of charge estimation algorithms for LiFePO4 batteries used in electric vehicles

One of the most important aspects in battery management systems (BMS) in electric vehicles is the state of charge (SOC) estimation. SOC needs to be accurately determined for safety and performance reasons but cannot be measured directly due to the flatness and hysteresis of the open circuit voltage (OCV) curve of Lithium-ion chemistries as LiFePO4. The classical approach of current integration (Coulomb counting) cannot solve the problems of accumulative error and inaccurate initial values, thus advanced estimation algorithms are applied to determine the sate of charge. In this work, three model-based state observer designs including Luenberger observer, Extended Kalman Filter (EKF) and Sigma Point Kalman Filter (SPKF) are carried out and studied. These estimation approaches are verified using measurement data acquired from commercial LiFePO4 cells. In addition, computational tests analyze the systems performances in terms of tracking accuracy, estimation robustness against temperature uncertainty, sensor drift, and convergence behavior with an initial SOC offset.

A novel way to calculate energy efficiency for rechargeable batteries

A new method to calculate energy efficiency for rechargeable batteries is proposed successfully and described in the study. The energy efficiency is divided into three categories, the energy efficiency under charge, the energy efficiency under discharge and the energy efficiency under charge–discharge. A key factor in calculating the energy efficiency is attributed to resolve the chemical energy stored in batteries (referred to as net energy hereafter). The net energy is stated with an equation of a function of the open circuit voltage (OCV) and the state of charge (SOC). Therefore, the relationship of OCV and SOC must be sought to solve the function. The OCV curve is computed by average of the charge curve and the discharge curve at a low rate. The quantitative relation of OCV to SOC is acquired by nonlinear fit. According to the method, LiFePO4 power batteries’ energy efficiencies are measured under the moderate current charging and discharging condition. The quantitative relations of the efficiencies are also analyzed for the batteries.

Probing the Radiative Limits of III-V Quantum Wells

High-voltage InGaAs quantum well devices are shown to operate in a regime of suppressed radiative recombination. A novel extended heterojunction structure is employed to reduce non-radiative recombination and expose the limiting n=1 component of the diode current. Short circuit current versus open circuit voltage curves derived from illuminated current-voltage measurements on several sets of InGaAs quantum well solar cells are analyzed, and the underlying saturation current densities extracted. Diode currents lower than those expected from detailed balance theory are observed, and possible mechanisms for the apparent suppression in radiative recombination are discussed.

Demonstration and Study of Photovoltaic Performances of InGaN p-i-n Homojunction Solar Cells

We reported on the InGaN p-i-n homojunction solar cells with In contents of 0.02 and 0.12. Under the same illumination of Xe lamp, In0.02 Ga0.98N cell exhibited a fill factor (FF) of 67.8%, a higher open-circuit voltage (Voc) of 2.15 V while In0.12Ga0.88N cell showed a FF of 64.8% and a lower Voc of 1.35 V. The measurements of atomic force microscopy (AFM) images and leakage currents revealed that V-shaped defects, which are known to cause the increase in reverse current, were the main factor dominating the Voc of In0.12Ga0.88N cells. Short-circuit current versus open-circuit voltage (Jsc - Voc) curves were consistent with the characteristics expected from the current-voltage equation. Relative external quantum efficiencies (EQEs) were also measured and showed strong dependence on V-shaped defects. These results indicate that defects in bulk InGaN has a negative impact on the photovoltaic performances of solar cells based on III-nitrides.

Electrodeposition of aluminium film on P90 Li–Al alloy as protective coating against corrosion

In this paper we report on the electrodeposition of thin aluminium layers on P90 lithium–aluminium alloy at room temperature from a chloroaluminate ionic liquid (1-butyl-3-methyl imidazolium heptachloroaluminate [BMIm]Al 2Cl 7). We found that the treatment of the P90 sample's surface is a key point to obtain good quality coatings. On freshly mechanically polished surfaces, thin (about 24 µm), homogeneous and dense aluminium layers were obtained at 10 µm h − 1 deposition rate. Finally, the corrosion resistance of the uncoated and Al-coated samples was investigated by means of electrochemical techniques such as open-circuit voltage curves, impedance spectroscopy and potentiodynamic polarization in 3.5 wt.% NaCl aqueous solution. We found that the protective aluminium layer significantly reduces the corrosion rates of the P90 Li–Al alloy.

Silver solid-state batteries: A 33 years storage realities

Solid-state, Ag/Me 4NI n ( n = 5 or 9) batteries have been tested in terms of changes of open circuit voltage, internal resistance and constant-load discharge curves after a storage time of 33 years at 23 °C. The results are in agreement the original shelf life projections, this confirming that these solid-state batteries should survive 50 years storage at 20–25 °C, and still deliver 50–60% of the initial available energy. To our knowledge, such an exceptional shelf life is an unique feature in the battery scenario which gives to these solid-state systems a renewed interest as reliable, long-life reference systems.

First-Principle Study of the Intercalation Process in the LixV2O5 System

A theoretical study of the lithium intercalated LixV2O5 system has been performed using a dual approach, based on ab initio calculations and experimental data. Two main aspects have been investigated: the atomic structure of each phase and the voltage of a lithium battery with a positive electrode made of LixV2O5. This approach leads to proposal of the full atomic arrangement for the different phases obtained during the reaction. Particularly, a structural arrangement is proposed for the debated ω-Li3V2O5 phase, based on a full simulation of its X-ray powder diagram. For the first time, an antiferromagnetic ordering is envisioned for ζ-Li2V2O5. Finally, a very good simulation of the experimental open circuit voltage (OCV) curve of the battery, from x = 0 to x = 3, is obtained when the magnetic interactions are considered.

Electrochemical and thermodynamic studies of nickel electrodes in alkaline electrolytes

The nickel electrode is widely used as a positive electrode in rechargeable alkaline batteries. The electrochemical behaviour of nickel hydroxide powders in several kinds of electrolyte is investigated. The open-circuit voltage (OCV) of the nickel oxide electrode in 3 M KOH displays an S-shaped curve in the reduction process. On the other hand, the nickel oxide electrode in 3 M NaOH and 3 M LiOH shows two-step reduction OCV curves. In the first stage, the OCV curves are S-shaped, while in the second stage, the OCV curves are L-shaped. The S-shaped stage of the OCV curve is examined by using thermodynamic considerations. The thermodynamic simulation and experimental results are in fairly good agreement with one fitting parameter φ/RT; φ is an interaction energy parameter (J mol −1) and RT has the usual significance. The interaction energy parameter ( φ) is found to increase in the order 3 M LiOH < 3 M NaOH < 3 M KOH. This concluded that the alkaline cation intercalated into the nickel oxide lattice decreases the interaction energy parameter ( φ).

Fabrication of Thin Film LiCo0.5Ni0.5 O 2 Cathode for Li Rechargeable Microbattery

thin film cathodes were fabricated by electron beam evaporation and postannealing in oxygen atmosphere. As‐deposited film showed almost amorphous characteristics, but included some crystalline phases. Hexagonal phase of was formed in the films annealed between 500 and 700°C. The crystallinity of the film was improved as the annealing temperature increased to 700°C. Open‐circuit voltage (OCV) curves were measured. Especially, the film annealed at 700°C for 10 min showed a similar OCV curve to that of bulk powder cathode. It can be suggested that thin film is suitable for the cathode of Li rechargeable microbattery.

Lithium insertion into M 2+-V 2O 5 bronzes ( M = Ni, Mn, Co, Cu)

Electrochemical lithium insertion into α-type vanadium oxide bronze M 2+-V 2O 5 (M = Ni, Mn, Co, Cu) of orthorhombic system was studied, by comparing with V 2O 5. The amount of lithium inserted into M 2+-V 2O 5 bronzes up to the second plateau was smaller by about 0.15 mol than the case of V 2O 5 on open circuit voltage (OCV) curves and discharge curves. These results prove that M 2+ cations in the bronze are placed in the same sites as lithium between the layer of V-O polyhedra and that the number of foreign ions which can be inserted is governed by the number of sites.

Lithium insertion into vanadium oxide bronze containing nickel

Electrochemical insertion of lithium ions into V 2O 5 bronze containing nickel (NiV 2O 5, Ni V = 0.075 ) was studied by comparing with V 2O 5. The difference in the amount of lithium inserted up to the second plateau was about 0.15 between NiV 2O 5 and V 2O 5 on open circuit voltage (OCV) curves. The broadened reduction and oxidation peaks in cyclic voltammogram, indistinct plateaux in discharge curve, and wide gap between OCV and discharge potential observed on NiV 2O 5 suggested that nickel ions in the bronze are placed in the same sites as lithium and disturb lithium diffusion along the channels of V 2O 5 structure. The present results implied that two factors, charge balance and lattice sites, governed the insertion of foreign ions, such as Li + and Ni 2+, into V 2O 5 lattice.

Characterization of silver vanadium oxide cathode material by high-resolution electron microscopy

The nature of the discharge reaction of lithium/silver vanadium oxide batteries was investigated. The lithiation of silver vanadium oxide, which has the formula Ag 2− y V 4O 11, proceeds by a multistep reaction, as indicated by the open-circuit voltage curve. The first step in the discharge reaction involves reduction of silver and separation of the oxide into two phases of differing composition. Electron diffraction of lithiated materials of various compositions suggests that the layered structure of the oxide is maintained, but with an increased amount of stacking disorder. High-resolution electron micrographs of lithiated Ag 2− y V 4O 11 at atomic resolution could not be obtained because of sample decomposition in the electron beam.

V 2O 4S — a new transition metal oxysulfide as positive for lithium batteries

In an attempt to combine the advantages of both oxides and sulfides in their use as positives in lithium batteries, we are investigating the electrochemical performances of new transition metal oxysulfides. A new amorphous vanadium oxysulfide can be prepared by room temperature reaction between aqueous solutions of a vanadyl salt and sodium sulfide. Chemical analysis and thermogravimetric analysis (TGA) experiments are consistent with the formula V 2O 4S·2H 2O and show complete dehydration at 150 °C. Electrochemical tests have been performed on lithium button cells containing the dried vanadium oxysulfide as positive. The open-circuit voltage (OCV) curve shows a lower potential than for the parent V 2O 5 compound but a low polarization is observed for the cell containing V 2O 4S. The cells can be cycled between 1.5 and 4.0 V with one lithium per vanadium atom, the mean voltage being 2.4 V, at regimes C/12 and C/24. This behaviour corresponds to a capacity of 270.9 A h/kg and an energy of 650 W h/kg. To date, 21 cycles have been performed with a capacity loss lower than 10%.

Synthesis of LiCoO 2 from cobalt—organic acid complexes and its electrode behaviour in a lithium secondary battery

Well-crystallized, layered LiCoO 2 has been prepared by heating cobalt—organic acid complexes (such as malic acid and succinic acid) at 900 °C in air after preheating at 400 °C (2 h) and at 650 °C (6 h). LiCoO 2 obtained by this method shows a high (003) peak intensity and low (104) or (101) intensities in X-ray diffraction (XRD). The first discharge capacity of LiCoO 2 obtained from this method in ester-based electrolyte is 132 mA h g −1 on cycling between 4.3 and 3.7 V. The value is larger than that obtained by the conventional method. X-ray diffraction studies and open-circuit voltage curves show the presence of at least two types of reaction. A two-phase reaction occurs in the region of 0.71<χ <1.0 in Li xCoO 2. The lithiation proceeds as a homogeneous reaction together with expansion of the c-axis in the region of 0.47<χ<0.71. The expansion of the c-axis againstΔχ at x=0.56 corresponds well with the voltage jump observed in the charge/discharge curves.