Batteries open-circuit voltage

Open circuit voltage is the voltage across the terminals of a cell or battery when no external current flows. It is usually close to the thermodynamic voltage for the system. 

Likewise, the battery voltage is increased from its open circuit voltage on charge. 

Fig. 6. Discharge behavior of a battery where is the open circuit voltage (a) current—potential or power curve showing M activation, ohmic, and M concentration polarization regions where the double headed arrow represents polarization loss and (b) voltage—time profile.

To calculate the open circuit voltage of the lead—acid battery, an accurate value for the standard cell potential, which is consistent with the activity coefficients of sulfuric acid, must also be known. The standard cell potential for the double sulfate reaction is 2.048 V at 25 °C. This value is calculated from the standard electrode potentials for the (Pt)H2 H2S04(yw) PbS04 Pb02(Pt) electrode 1.690 V (14), for the Pb(Hg) PbS04 H2S04(yw) H2(Pt) electrode 0.3526 V (19), and for the Pb Pb2+ Pb(Hg) 0.0057 V (21). 

Typical dimensions for the /5-alumina electrolyte tube are 380 mm long, with an outer diameter of 28 mm, and a wall thickness of 1.5 mm. A typical battery for automotive power might contain 980 of such cells (20 modules each of 49 cells) and have an open-circuit voltage of lOOV. Capacity exceeds. 50 kWh. The cells operate at an optimum temperature of 300-350°C (to ensure that the sodium polysulfides remain molten and that the /5-alumina solid electrolyte has an adequate Na" " ion conductivity). This means that the cells must be thermally insulated to reduce wasteful loss of heat atjd to maintain the electrodes molten even when not in operation. Such a system is about one-fifth of the weight of an equivalent lead-acid traction battery and has a similar life ( 1000 cycles). 

Table 1. Open-circuit voltages of battery systems with zinc anodes...

The electrolyte is usually 40% KOH aqueous solution. The open-circuit voltage of this system is 0.90 V. The battery can be used and stored in a wide range of temperatures, from —55 to 80 °C, due to low solubility of cadmium oxide in concentrated KOH solutions [342]. 

While irradiating the experimental agent A thin film with a xenon lamp, the voltage-current properties were measured. In this way solar battery properties of a short-circuit current of 43 pA/cm2 and a open-circuit voltage of 1.75 V for this material were obtained. Testing results are provided in Table 2. 

Calculate the free energy change (heat change) of the cell reaction (AH) in calories for two battery systems (a) A lead-acid cell with an open-circuit voltage of 2.01 V at 15 °C and a temperature coefficient of resistance (dE/dT) of 0.0037 V/K. (b) A Zn-Hg cell (Clark cell) with an open-circuit potential of 1.4324 V at 15 °C and a temperature coefficient of 0.00019 V/K. (Bhardwaj)... 

Kinetic processes in an electrochemical reaction must be considered when current is extracted from a battery, that is, when the current passed through an external circuit is different from zero. In this case, while current is removed from the battery, the equilibrium voltage or open circuit voltage falls because of electrode polarization or overvoltage [6,8,10,66,123,124], This electrode polarization effect occurs owing to kinetic limitations experienced by the reactions, and because of other processes taking place during the production of current flow. 

First-principles calculation on lithium transition metal oxides of positive electrodes for lithium-ion batteries have been done by many researchers [17-20]. In general the open-circuit voltage EocvM depends on the difference in the Li chemical potential between anode Li metal and cathode. In this paper, we have investigated the possibility of using the metal oxide powders for anodic electrode as active materials and find out their electrochemical performance through the calculation. The first-principles calculation in this paper for the voltages was carried out as follows ... 

An AFC combined with a lead acid battery has been used in a hybrid vehicle. Between operating times the cell was shut down by using the battery to drain the KOH electrolyte. This technique can improve the life expectancy enormously by protecting the fuel cell from a high open circuit voltage, which otherwise could induce carbon oxidation processes to produce carbonates that would destroy the matrix electrolyte. 

Since it is impossible to measure the individual electric potential differences at the phase boundaries, we shall hereinafter speak only in terms of the difference in electric potential across the two terminals connected to the electrodes of the battery. When in a battery the current is not flowing or tends to zero, the measurable potential difference across the two terminals is called the open-circuit voltage (OCV), fJc, and it represents the battery s equilibrium potential (or voltage). Since it is related to the free energy of the cell reaction, the OCV is a measure of the tendency of the cell reaction to take place. Indeed, while the conversion of chemical into electric energy is regulated by thermodynamics, the behavior of a battery under current flow (the current is a measure of the electrochemical reaction rate) comes under electrochemical kinetics. 

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