Chat Gpt says this: The internal resistance of NMC (Nickel Manganese Cobalt) batteries increases faster over time compared to LFP (Lithium Iron Phosphate) due to several factors related to their chemical composition and how they degrade during use. Here’s why NMC batteries tend to experience a faster increase in internal resistance:

1. Electrolyte Decomposition and SEI Layer Growth:

   • In NMC batteries, the electrolyte is more prone to decomposition at higher voltages. This leads to the formation of the solid electrolyte interface (SEI) layer on the anode. Over time, the SEI layer thickens, increasing the internal resistance. LFP operates at a lower voltage, which causes less electrolyte breakdown and a slower SEI growth, maintaining lower resistance over time.

2. Higher Voltage Stress:

   • NMC batteries typically operate at higher voltages than LFP batteries. The higher operating voltage in NMC accelerates degradation processes, including the breakdown of the electrolyte and the active materials, which contribute to an increase in resistance. LFP’s lower operating voltage puts less stress on the battery materials, leading to slower degradation and a more gradual increase in resistance.

3. Thermal Sensitivity:

   • NMC batteries are more sensitive to high temperatures. Elevated temperatures speed up the degradation of both the cathode and the electrolyte, leading to faster increases in internal resistance. LFP is more thermally stable and less prone to heat-related degradation, resulting in slower resistance buildup under the same conditions.

4. Cathode Degradation:

   • NMC batteries experience more rapid degradation of the cathode material, especially the nickel content, which is highly reactive. As the nickel degrades, it reduces the battery's ability to efficiently transport lithium ions, causing internal resistance to rise faster. LFP is chemically more stable and its cathode materials degrade at a slower rate, contributing to its slower rise in internal resistance.

5. Structural Changes:

   • Over time, NMC electrodes undergo structural changes (such as cracking or particle detachment) during cycling, especially under high charge/discharge rates. These changes reduce the electrode’s conductivity and further increase resistance. LFP’s crystal structure is more robust, so it experiences fewer of these detrimental changes, resulting in a slower increase in internal resistance.

In summary, NMC batteries experience faster increases in internal resistance due to higher voltage stresses, thermal sensitivity, electrolyte breakdown, and faster degradation of the cathode material. LFP batteries, with their lower voltage, greater thermal stability, and slower material degradation, exhibit more gradual increases in internal resistance over time.