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The difference and correlation between battery round-trip efficiency (RTE) and health state of health (SOH)

The round-trip efficiency of a battery, also known as RTE (Round Trip Efficiency), represents the percentage of energy that the battery can utilize (output) to its stored energy. That is, if the energy input for charging the battery is Ein and the energy that can be utilized (output) is Eout, then its round-trip efficiency RTE=Eout/Ein. RTE is expressed in percentage form, with higher values indicating higher energy conversion efficiency and less loss of the battery. High round-trip efficiency means that the battery can store and release energy more effectively during the charging and discharging cycle, providing longer usage time. For example, if a battery stores 10 kWh of energy during charging, but can only recover 8 kWh during discharge, the battery's round-trip efficiency is 80%. The round-trip efficiency (RTE) is an important indicator for measuring the energy storage efficiency of batteries, indicating the magnitude of energy loss during the process of storing and releasing energy. RTE is influenced by various factors, such as battery model, temperature, charging and discharging rates, and so on. Continuously evaluate RTE and identify reasons why reducing energy loss may improve battery efficiency and lifespan. Generally speaking, the round-trip efficiency of batteries decreases with the increase of battery usage and charging and discharging times. This is because during each charging and discharging cycle of the battery, energy loss occurs due to internal chemical reactions and other losses during operation. These energy losses include internal resistance effects, voltammetry effects, electrochemical reactions, and electrode material losses, among others. In order to slow down or prolong the decrease in battery round-trip efficiency, some measures can be taken, such as lowering the temperature of the battery, lowering the charging and discharging rate of the battery, and implementing balanced charging management, which can effectively maintain the round-trip efficiency of the battery. [State of Health (SOH) of Battery] The State of Health (SOH) of a battery represents the percentage of energy that the battery can utilize (output) to its rated energy. The health state of a battery (SOH) refers to the degree to which it can maintain its initial design performance (such as capacity, voltage, internal resistance, etc.) during long-term use. A higher SOH value indicates that the battery's performance and lifespan are still good, while a lower SOH value indicates that the battery has experienced a certain degree of capacity loss and performance degradation. Specifically, health status refers to the ability of a battery to provide its originally specified functions and performance, that is, the battery can still maintain expected performance parameters such as capacity, voltage, and energy density. For example, a lithium-ion battery that has been placed for a period of time may experience some capacity loss, and some (or all) electrode materials may be released, thereby weakening the electrode reaction rate of the battery and resulting in some performance issues. By conducting SOH testing on the lithium-ion battery in use, the health status of the battery can be determined, which in turn determines whether the battery needs to be replaced or repaired. The difference and connection between RTE and SOH   The connection between RTE and SOH is that they are both indicators used to evaluate battery performance and health status. RTE mainly focuses on the energy conversion efficiency of batteries, measuring the degree of loss of batteries during charging and discharging processes. SOH focuses on the capacity and performance degradation of batteries, providing information about their current health status.   In general, higher RTE and SOH values indicate that the battery is in a good state, with less performance degradation and higher energy conversion efficiency. Lower RTE and SOH values may indicate a decrease in battery performance and capacity, requiring attention to maintenance and replacement timing. Assuming that after multiple charging and discharging cycles, SoH=80%, RTE=92%, and the actual maximum energy output of the battery is 73.6% of the rated capacity (=0.8 * 0.92).   In summary, RTE and SOH are two important battery performance evaluation indicators. RTE focuses on the energy conversion efficiency of batteries, while SOH focuses on the health status and performance degradation of batteries. By monitoring and evaluating these two indicators, it is possible to better understand the working status of batteries, take appropriate maintenance and management measures, and extend battery life and improve performance.