Formation Process Of The Silicon Negative Electrode SEI Film And The State Of Charge Estimation For Li-ion Battery

As energy issues become more and more prominent,li-ion batteries are attracting more and more attention.The biggest problem that restricts the development of li-ion battery is the capacity of battery,especially the negative electrode.Silicon has attracted more and more attention due to its high theoretical specific capacity(4200mAh g^-1),low lithium intercalation potential?0.37m V Li/Li⁺?,its huge reserves and mature production technology.However,during the process of lithium intercalation and deintercalation from the silicon,the violent volume change not only cause the collapse of the negative material and the instability of the electrode structure,but also makes the SEI film continuously broken and regenerated,thus the electrochemical performance of the anode is greatly reduced.The main stage of the SEI film formation in the battery production is the formation stage.How to form a stable and uniform SEI film on the silicon surface,and then reduce the rupture and regeneration of the SEI film in the process of lithium intercalation,which can improve the battery performance.In this paper,the SEI membrane of the silicon anode material is regulated by controlling the related parameters in the process.Besides,the cycle performance,cycle efficiency and rate performance of the battery are improved.This work chose the silicon negative electrode materials and battery fabrication processes used in the present laboratory firstly,which selected the experimental materials and the fabrication process with stable performance to ensure the consistency of the battery.Base on this,the existing activation process was improved to explore the effect of the current and cycle times on the performance of SEI film,and then changed the existing activation process accordingly.Secondly,we tried to make a new process,which holds the cell at constant potential during the activation stage,to explore the performance of the SEI film and the effect on the battery performance,finally,optimized the activation process.In view of the laboratory experiment and the experimental requirements,we selected the battery model which can fully perform the physical and chemical performance of the battery firstly,and combined the estimation algorithm to make an algorithm to improve the estimation effect,and then compared the estimation accuracy and robustness of the algorithm.The research shows that:1)the cell performance,which was made by process two based on silicon based negative electrode material S400,is more stable.It has the high material capacity and good performance consistency,which can be used for follow experiment;2)the traditional activation process of the laboratory is the three cycle with small current?0.05C?,and the SEI film mainly formed at the first cycle,the subsequent cycle is only a supplement to the SEI membrane.During this process,the current density influenced the SEI film performance,and the 0.02C current density has the most obvious effect.3)under constant voltage environment,it provided a better condition for the formation reaction of SEI film,which can produce more stable composition,more compact structure and better elastic SEI film.Besides,the best performance of the SEI film is under the 0.4V voltage.4)the combined model of the battery can accurately simulate the characteristics of the battery,at the same time,the genetic algorithm and particle filter can accurately estimate the battery state of charge and have strong robustness,which can fully meet the requirements of the battery state of charge estimation.The innovations of this work are as follows:1)in this paper,we selected the promising silicon negative electrode materials and the less involved battery technology,it means the novel angle;2)as to the inherent negative electrode activating process,we improve it and improv e the efficiency of the experiment;3)design a new cell activation process based on the existing experimental results and the literature content,improved the experimental efficiency and the accuracy and stability of the experimental results;4)the theoretical research content in the paper plays a better guiding role in the industrialization application process of silicon based negative electrode material.5)put forward a way to solve the problem of selecting suitable battery models and combining general performance algorithms to achieve specific requirements.