What is the reason for the maximum capacity drop of the lithium battery when it is used too much?

What is the reason why the maximum capacity of lithium batteries decreases with the increase in usage? Common household rechargeable batteries, such as lithium batteries and nickel-cadmium-nickel metal hydride batteries, whose maximum capacity decreases with the increase in usage time . What is the reason? Let Yunfan lithium battery experts take you to discuss: internal and external reasons: 1. Internal reasons (1) In the electrode, repeated charging and discharging can reduce the surface products of electrode activity and increase the current density. Polarization is added; the structure of the active substance is changed. The electrical contact of the active particles deteriorates or even drops. Corrosion of electrode data (including collector fluid); currently commonly used battery negative electrodes are graphite, anodes LiCoO2, LiMn2O4, lithium iron phosphate batteries form a layer of SEI (solid electrolyte membrane) on the surface of the electrode with some initial electrolyte, the composition of which is mainly ROCO2Li Carbonic acid (EC and PC cyclic recovery products), ROCO2Li and ROLi carbonic acid (DEC, DMC chain products) recovery, Li2CO3 (residual water and ROCO2Li reaction products), if LiPF6 is used, high-frequency residuals and SEIROCO2Li, make SEI important to LiF and ROLi.SEI Li + conductor, when the lithium carbon electrode is released, the volume change is small, but even if it is small, its internal pressure will negatively break, exposing the new carbon appearance and reacting the SEI film with the solvent, thereby forming lithium ions and Electrolyte loss, and the degree of positive data in a specific active material is fluffy, please do not touch the loss correction permanent structure, therefore, the consumption of positive and negative constitutes a decline in capacity; in addition, the added SEI will form the resistance layer of the interface Frame, the polarization potential of the electrochemical reaction is added, and the function of the battery is attenuated in the electrode. With the response of charging and discharging, the function of the adhesive will gradually decrease, the strength of the adhesive will decrease, and the electrode data will decrease. .Copper foil and aluminum foil are commonly used negative and positive collector liquids, both of which are prone to corrosion. Corrosion products accumulate on the surface of the collector liquid film, which increases internal resistance. Copper ions can also form dendrites and penetrate the gaps. Make the battery useless. (2) In the electrolyte solution, the differentiation of the electrolyte or conductive salt leads to the decrease of its conductivity, and this differentiation constitutes the interface passivation; the liquid electrolyte of the lithium battery is generally composed of solutes (such as LiPF6, LiBF4, LiClO4 and other lithium salts) , Solvent and special additives. The electrolyte has good ionic conductivity and electronic insulation, and conducts current between the positive electrode and the negative electrode. After the first charge and discharge, overcharge and overdischarge, the electrolyte degrades after a long period of time The effect will occur in the lithium battery. With the generation of gas, the gas composition is relatively chaotic. It cannot eliminate the battery after a certain reaction. Then add the number of charge and discharge of the battery. Due to the oxidation and corrosion of the electrode data, part of the electrolyte will be consumed. The electrolyte is insufficient and the electrodes cannot be completely flushed into the electrolyte, which leads to incomplete electrochemical reactions, and the battery capacity cannot meet the planning requirements. (3) The barrier is blocked or damaged, and the internal short circuit of the battery is used to protect the battery. The positive and negative electrodes are separated to prevent a direct short circuit between the north and south poles. During the cycle of lithium batteries, the separator gradually dries, and failure is an important reason for the early decline of battery function. This is important because the electrolyte is in the barrier Drying, the resistance of the solution increases, the electrochemical stability and mechanical properties of the barrier decrease, and the wettability of the electrolyte decreases during repeated charging. Due to the dry gap, the ohmic resistance of the battery increases, resulting in incomplete discharge, and the battery repeatedly The overcharge capacity is large, and the battery capacity cannot be restored to the initial state, which greatly reduces the discharge capacity and service life of the battery. 2. External reasons (1) fast Fast charging and discharging In the case of fast charging, the current density is too large, the negative electrode polarization is serious, and the accumulation of lithium is more obvious, making the copper foil brittle and prone to cracks at the boundary between the copper foil and the carbon active material. The spontaneous winding of the battery is limited by the fixed space, and the copper foil cannot be stretched freely to cause pressure. Under the application of pressure, the original cracks expand and expand, and the copper foil breaks due to insufficient expansion space. (2) Temperature When the temperature is significantly higher than room temperature, the first consideration is the thermal stability of the organic electrolyte, including the thermal stability of the organic electrolyte itself and the thermal stability of the electrode and the electrolyte for mutual use. It is generally believed that the impact of the positive electrode/organic electrolyte reaction on the safety of kk ion batteries is an important factor. Since the reaction kinetics of the positive electrode and the electrolyte is very fast, the heat resistance of the entire battery is controlled. If the ambient temperature of the battery is high enough to cause a positive electrolyte reaction, it will cause thermal runaway of the battery, and even fire and explosion. The size of the discharge current directly affects the discharge capacity of the lithium battery. In the case of high-current discharge, there is not only severe electrolyte interface polarization, but also diffusion polarization of the active body, that is, intercalated ions and electrodes. (3) Long-term deep charging and discharging must be transferred from the internal structure. One is the formation of excessive evaporation of electrolyte, and the other is that the negative electrode of the lithium battery excessively responds to the change of the dielectric film, and its composition ability is demolded, which constitutes a permanent capacity loss; The important thing comes from the voltage stability in the middle of the night and the rise of the grid voltage. This charger has stopped charging. After the voltage rises, it will continue to charge. The excessive charge leads to the loss of the ability to change the data structure of the positive electrode of the battery, the differentiation of oxygen and electrolyte, and the violent oxidation reaction. And combustion explosion; electrolyte organic solvent/electrolyte lithium salt differentiation; the precipitation of lithium ions in the negative electrode will cause the dissolution of the negative electrode copper ions, and the positive electrode will form copper dendrites. (4) Feeling and impact are generally due to the process, such as whether the welding is firm or not, whether the internal circuit planning is reasonable, and so on. Disclaimer: Some pictures and content of articles published on this site are from the Internet, please contact to delete if there is any infringement. Previous: Comparison of polymer batteries and liquid lithium batteries