However, it has been observed that on the surface of the negative electrode, a passivation layer gets formed, which provides protection by slowing down the kinetics of the reduction. This layer allows Li+ ions to diffuse but isolates the electrode's material contact with the electrolyte. Hence, we can say that the layer is electronically insulating while ionically conducting. This passivation layer enables the functioning of a Li-ion battery, and the instability of which is also a primary reason for the major reasons for loss of performance and the quick ageing of batteries. The stability and ease of formation of the SEI (Solid Electrolyte Interphase) layer are major considerations for the selection of anode materials.