Hello,
I want to be able to simulate one cycle to represent multiple ageing cycles (For example to simulate a battery aging over 800 cycles, I might only simulate 8 cycles with ageing factor of 100). For reference, this is how COMSOL’s lithium ion capacity fade model does it (see the time accelerating factor) https://doc.comsol.com/5.6/doc/com.comsol.help.models.battery.capacity_fade/models.battery.capacity_fade.pdf .
I’m having difficulty implementing this. What I have done is defined a parameter, tau, and modified the sei_growth.py file such that dLdt_SEI = tau * phase_param.V_bar_sei * j_sei / (self.param.F *phase_param.z_sei). I thought this would work, because from digging around in base_sei.py, it looks the lithium loss to SEI is calculated from the SEI thickness.
The resulting behaviour is unexpected. When I set tau=100, it does indeed result in much higher SEI thickness being formed. However, the capacity loss in Ah is lower for tau=100. During investigation, it appears that the loss of lithium per SEI formed is 100 times lower for tau=100 as compared to tau=1. The result is a lower capacity loss for tau=100 as compared to tau=1. I am not sure why this is, because the loss of lithium per SEI formed should be the same regardless of what tau is. I only multiplied tau into dLdt_SEI, so I am confused why the lithium inventory calculation is changing.
Anybody have any ideas?
Supporting info: here’s SEI thickness vs cycle number for tau=100 and tau=1, along with Loss of Lithium vs SEI thickness:
