Introduction to three parameters of lithium ion battery: internal resistance, capacity and power

　　(1) Internal resistance of lithium ion batteries The internal resistance of lithium ion batteries consists of factors that prevent lithium ions from moving from one electrode to another. Its important part includes the physical internal resistance of conductive parts; The inherent impedance of electrochemical materials such as motor materials, diaphragms and electrolytes; When there is current in the battery, obstacles for lithium ion movement are temporarily added; These three parts together constitute the main body of internal resistance. The internal resistance is most sensitive to temperature. The internal resistance will change greatly at different temperatures. One of the important reasons for the low temperature performance degradation of batteries is the excessive internal resistance of batteries at low temperatures. As a power supply, the smaller the internal resistance, the better. Especially in the case of power supply applications, small internal resistance is a necessary condition

　　(2) Capacity The capacity of a lithium ion battery, the measurable capacity, refers to the maximum power that can be charged and discharged within the reasonable maximum and minimum voltage range of the battery. Before loading the monomer onto the vehicle, the capacity of the monomer can be measured by charging and discharging. Once in the vehicle, the battery capacity can only be estimated by algorithm. In the battery management system BMS, the accurate estimation of SOC is an important indicator to measure its design level. The capacity of monomer is obviously affected by aging degree. As we all know, when the capacity decays to the limit value, that is, when the battery is eliminated, it can be seen that there is an absolute correlation between the two. Secondly, the capacity is also affected by temperature. At low temperature, the activity of active substances decreases, the available ions decrease, and the capacity inevitably decreases

　　(3) To be exact, the power here should be the specific power, which is the charging and discharging power capacity of a single object, or the charging and discharging power capacity of a battery per unit mass or volume. The power lithium-ion battery is a power lithium-ion battery. Its important feature is to support high rate charging and discharging, up to 10C. The important parameter to consider is the specific function (wkg). Whether lithium ion batteries can be charged and discharged with high power has become an important issue in the design. It is also made of lithium iron phosphate or ternary materials. The power performance of the battery can be adjusted by adopting technological means, changing the electrode thickness or adding additives, adjusting the active substance structure, electrolyte performance and electrode SEI film performance. In general, power performance and energy density cannot coexist. If the same material pursues high power, it will sacrifice part of the energy density

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