1. Condensed phase flame retardant (carbonization)：

Role of phosphorus: decomposes at high temperature to generate acidic substances such as phosphoric acid and polyphosphoric acid, catalyzes the dehydration of polymers into carbon, and forms a dense carbon layer. The carbon layer isolates oxygen and heat, inhibiting the release of combustible gases.

Role of phosphorus nitrogen group (Phosphazene): The phosphorus nitrogen structure generates a cross-linked nitrogen-containing carbon layer (such as N-P-O structure) at high temperature, which enhances the thermal stability and mechanical strength of the carbon layer.

2. Gas phase flame retardant (free radical capture):

PFPN can generate fluorine and phosphorus free radicals at high temperature, interrupting the combustion chain reaction. Fluorine releases fluorine free radicals (F·) when the compound decomposes, captures active free radicals (such as H·, HO·) in the combustion chain reaction, interrupts the combustion reaction; and decomposes to produce non-combustible gases such as NH₃ and N₂, diluting the concentration of combustible gases and reducing the combustion intensity.

3. Synergistic effect:

The three elements of phosphorus, fluorine and nitrogen work together to form a double barrier of "condensed phase carbonization + gas phase flame suppression", which significantly improves the flame retardant efficiency.

PFPN protective electrode action mechanism: The molecular structure of PFPN contains elements such as phosphorus, fluorine and nitrogen. Its high HOMO energy level (-7.44 eV) makes it preferentially oxidized and decomposed in the electrolyte over conventional solvents (such as EC, DMC), thereby forming a protective layer on the electrode surface.

PFPN can interact with lithium salts (such as LiPF6) in the electrolyte. This interaction may change the decomposition pathway and decomposition products of lithium salts, making it easier to participate in the film-forming reaction on the electrode surface. For example, the deposition of fluorine-containing compounds on the electrode surface helps to form a more stable film.

4. Practical application and effect：

Improve battery performance:

Lithium batteries with PFPN added have shown significant improvements in cycle performance, rate performance, and low temperature performance. For example, adding a certain proportion of PFPN can make the battery cycle stably under high-rate charge and discharge, and the battery cycle life and capacity retention rate are improved.

Enhanced safety:

The flame retardant properties of PFPN effectively eliminate the flammability risks of lithium batteries and improve the overall safety of the battery. At the same time, PFPN can also improve the thermal stability of the battery, so that the battery can maintain stable performance under extreme conditions such as high temperature or short circuit.

In summary, ethoxy (pentafluoro) cyclotriphosphazene PFPN, as a multifunctional lithium battery additive, plays an important role in improving battery performance and safety. With the continuous development of lithium battery technology, PFPN is expected to be widely used in more fields.