In constant potential intermittent titration (Pitt), a constant voltage is applied at each potential step to test the change of current, and then the diffusion coefficient is calculated accordingly. Thus, the ion concentration at the surface can be obtained.
When the current decreases to the set value, the test of each step is terminated, and then a new potential step is applied to test the current change of the next step.
Figure 1.1 shows the change of current of cathode material LiMn2O4 with potential in lithium secondary battery.
Pitt results can be understood by studying the linear behavior of the current time curve. If the active material is spherical, the diffusion coefficient can be calculated with the transition time (TT) according to the following equation:
Where, I represents current; T is the test time; R1 is the radius of the active material; Is the diffusion time;
Is the power of each step.
LiFePO4 is a good cathode material for lithium-ion batteries, which is cheap, non-toxic and environmentally friendly. The researchers used Pitt technology to test the diffusion coefficient of lithium ion in LiFePO4 in different lithium embedded states.
There are two possible reasons for analysis: first, there is an “activation process” in the active material, in which the diffusion coefficient will increase with the increase of lithium ion insertion; second, with the increase of lithium ion insertion, the material gradually changes from single-phase to two-phase coexistence region, resulting in different diffusion coefficients.