The ideas of ECSD and 2-D Cell Ageing Mechanism Analysis help us to understand pack capacity evolution from a system point of view. By introducing the anode LLI, the analysis and experiment results successfully explain why battery pack life is always shorter than single cell life.
A lithium-ion battery (or battery pack) is made from one or more individual cells packaged together with their associated protection electronics (Fig. 1.8). By connecting cells in parallel (Fig. 1.9), designers increase pack capacity. By connecting cells in series (Fig. 1.10), designers increase pack voltage.
How is a lithium-ion battery based on a physics-based cell design?
The cell design was first modeled using a physics-based cell model of a lithium-ion battery sub-module with both charge and discharge events and porous positive and negative electrodes. We assume that the copper foil is used as an anode and an aluminum foil is used as a cathode.
Thus, lithium-ion battery packs often include controls to prevent charging at excessively low or high temperatures. Over-discharging lithium-ion cells can cause damage to current collectors, and ultimately electrodes, leading to compromised performance or increased risk of thermal runaway.
What happens if a lithium ion battery reaches a threshold voltage?
A lithium-ion cell in such a state of deep discharge will likely require low charging currents until the cell reaches some threshold voltage. Thus, lithium-ion battery packs often include controls to limit charge currents until a desired voltage threshold is reached.
How many series elements are in a lithium ion battery pack?
For example, a lithium-ion battery pack marked as 10.8 V nominal, 7.2 Ah can be assumed to contain three series elements (3 × 3.6 V = 10.8 V), with each series element containing 7.2-Ah capacity.
Thus, it largely reduces the time and labor for battery pack investigation. The predicted capacity trends of the battery cells connected in the battery pack accurately reflect the actual degradation of each battery cell, which can reveal the weakest cell for maintenance in advance.