如何计算理论容量和实际容量等.pdf

Things covered: 1.Different kinds of voltages 2.Calculating battery capacity 3.Behavior of batteries away from equilibrium 4.Modified Peukert Plot 5.Ragone Plot Almost all examples in this class will be on a Li-ion battery where the negative electrode is Li-metal and the positive electrode is LiNi Co Mn O . The negative electrode reaction is: 1/3 1/3 1/3 2 The positive electrode reaction is: A schematic of the battery is shown below: The positive electrode material is made into a porous electrode. The particles themselves are not very conductive, so conductive additives, like carbon are added to increase the conductivity. The reactions occur at the electrode/ electrolyte interface and the Li enters the lattice of the oxide. Different Kinds of Voltages and ways of measuring them: You already know about equilibrium potential and overpotential. Few more voltages: 1 1.Open circuit voltage: voltage when the battery is not connected to an external load. Practically, you have a voltmeter with a high resistance so that the current draw is very small and you measure the voltage of the battery. This is taken to be the same as the equilibrium potential. You can typically calculate the equilibrium potential by looking at the thermodynamic tables. But, for batteries, this tends to be difficult to do because of the dependence on the activity coefficients. 2.Closed circuit potential: potential of the battery under a load. 3.Mid-point potential: Potential of the battery when its discharged to 50% of its capacity. 4.Cut off voltage: Voltage when the battery discharge (or charge) is stopped. For example, cutoff voltage on charge is ~4.3 V for a cell phone battery. State of Discharge is defined as 1.0 when the battery is fully discharge and 0.0 when the battery is fully charged. SOD=1-SOC (or state of charge). Below is an ex