Fujifilm Corp announced that it has succeeded in interpreting the chemical reaction mechanism related to (1) the reductive decomposition in the electrolyte of lithium-ion (Li-ion) rechargeable battery and (2) the formation of a film at the interface between the electrolyte and electrodes at the molecular level.

Though it is difficult to directly observe the chemical reaction mechanism, Fujifilm clarified it by using the "Kei" supercomputer to simulate the chemical reaction in collaboration with Japan's National Institute for Materials Science (NIMS).

The keys to the performance and safety of Li-ion battery are (1) the reductive decomposition of the electrolyte and (2) the formation of the SEI film (on the interface of the electrodes), which is formed by the decomposition of the electrolyte.

It has been known that the performance of the SEI film can be drastically improved by adding a small amount of additive. But it was difficult to clarify the chemical reaction related to the formation of the film because the reaction could not be directly observed.

This time, Fujifilm applied a calculation technique combining (1) the First-Principles Molecular Dynamics (FPMD) and (2) the "free energy calculation" to a Li-ion rechargable battery for the first time in the world. The FPMD is a molecular dynamics calculation using atomic force based on a quantum mechanical equation that does not use any empirical parameter. It deals with chemical bonding. And the free energy calculation calculates a chemical reaction in a liquid by calculating the activation free energy, reaction free energy and reaction path of an active chemical reaction.

For the simulation, Fujifilm used ethylene carbonate (EC) as an electrolyte material and vinylene carbonate (VC) as an additive. This time, it clarified (1) the process in which the EC and VC are reduced and decomposed, (2) the process in which the SEI film is formed by the reaction between EC and VC and (3) the mechanism that generates by-product gasses (CO, C2H4 and CO2) in those processes at the molecular level.

As a result, the company interpreted the new chemical reaction mechanism that forms the material of the SEI film by the reaction between (1) the molecules of the electrolyte reduced by electrons moving from the electrodes at the time of charging and (2) the molecules of the unreduced additive.