Why the voltage of lithium-ion batteries cannot exceed 4.2V

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The voltage of a lithium ion battery is determined by the electrode potential. Voltage, is a physical quantity that measures the energy difference of electric charges in an electrostatic field. The electrode potential of lithium ion is about 3V, and the voltage of lithium ion batteries varies with different materials. For example, a general lithium-ion battery has a rated voltage of 3.7V and a full-charge voltage of 4.2V; while a lithium iron phosphate battery has a rated voltage of 3.2V and a full-charge voltage of 3.65V. In other words, the potential difference between the positive electrode and the negative electrode of a lithium-ion battery in practical use cannot exceed 4.2V. Which is a requirement based on material and use safety. If the Li/Li+ electrode is the reference potential, μA is the relative electrochemical potential of the negative electrode material. μC is the relative electrochemical potential of the positive electrode material. And the interval Eg is the lowest electron unoccupied energy level and the highest electron occupied energy of the electrolyte. The difference between the levels. Then, it is the three factors of μA, μC and Eg that determine the highest voltage value of a lithium-ion battery.