Brief introduction of life model of graphite lithium ion battery

- Sep 06, 2016 -

Lithium ion battery is the most commonly used electronic equipment (such as mobile phone, notebook computer) by chemical energy storage devices and electric vehicles for lithium ion batteries we are very concerned about the life cycle of it (usually we believe that the capacity of the lithium ion battery remaining less than 80% of its life is over), because it directly we decided to use experience and cost.           

 

The failure mechanism of lithium ion battery is more complex, for example, in the process of charging and discharging cycle will cause the mechanical stress of the electrode, which will cause the particle breakage, which can lead to the battery life decline. In addition in the cycle process, the electrode and the electrolyte will be between the side effects of the mask SEI film thickness, resulting in battery capacity attenuation. SNL is a professional lithium battery supplier, which also is an electric bike battery manufacture/factory supplies 36v lithium Battery36v battery 48v battery48v lithium ion battery48v 10a and so on.

          

 

In general, the lithium ion battery life and many factors, such as the state of charge SOC, discharge rate and other factors, but these are generally described based on empirical data, but also the lack of appropriate model to predict the lifetime of lithium ion batteries. The scope of the use of life cycle and the lithium ion battery in SOC is closely related to the research, for example Hoke shows that when the electric vehicle lithium ion battery using the SoC range decreased from 70%-90% to 20%-40%, to improve the cycle life of nearly 4 years.

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And Watanabe for NCA materials research shows that the use of materials to reduce the range to 3.48-4.05V (30%-90% SoC), the cycle life of the material has been greatly improved. And the research on the NCM material shows that the minimum capacity decline of the material occurs in the vicinity of SoC 50%. So it is very necessary to establish a model to predict the different SOC application range, the corresponding cycle life, so as to provide guidance for the application of lithium-ion batteries in practice.

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Recently, the Saxena Saurabh team of University of Maryland in the United States to carry out a life model for commercial LCO/C batteries. Experiments using 1.5Ah soft package lithium ion battery, cathode materials were LiCoO2 and graphite, the laboratory at 25 DEG C in the temperature control box.           

 

Because of the battery capacity during the cycle will continue the decline, so every 50 to 100 times in the test part of the circulation, it is necessary to conduct a full cycle (in the range of 2.75V-4.2V to C/2 current measuring battery residual capacity) measurement of battery capacity, to ensure the circulation of the SOC value in the process of accurate control the range of SOC values, such as 20%-80%. if you need 4s battery, SNL offers 14.4v, 14.4v battery, 14.8v battery,14.4v Lithium battery,14.4v battery pack,14.8v li ion battery pack oem welcome.

          

 

From the experimental results, when the SOC range in the impact of the larger battery cycle. When the range of 40%-60% is SOC, the decline rate of the battery capacity is significantly smaller than that of the cell cycle between 20%-80% and 0%-100%.           

 

At the same time, from the test results we also noticed that when a small magnification (C/2) cycle, SOC cycle between 20%-80% and 0%-100%, began their battery degradation speed is close, but in 500, SOC battery capacity between 0-100% started its rapid decline. But when the magnification is increased (2C), the gap between the two is significantly smaller.           

 

We can also see that, regardless of which circulate in the range of SOC, high magnification, battery capacity decline is faster, which may be related to battery in high rate discharge, the battery temperature increases more (at higher temperature and battery capacity decline faster).           


When will use SOC adjusted to 0%-60%, and 40%-100% 20%-80%, from the test results, the range of SOC 0%-60% battery capacity decline rate is significantly lower than the other two in the range of SOC, after 700 cycles the capacity retention rate can reach more than 97%, which indicates that in the lower range of SOC failure the mechanism is different from the battery cycle in the high range of SOC battery.

 

Another test results showed that the life cycle has a significant impact on the scope of the use of median SOC battery test, Saurabh Saxena et al designed different application range of SOC, 0%-60%, 40%-100%, 40%-60% and 0-100%, we generally think of SOC is smaller for smaller battery capacity decline, but in the actual test found that the battery cycle life of 0%-60% and 0%-100% is better than 40%-60% and 40%-100%.           

 

The median SOC were 30% and 50%, and the median SOC were 50% and 70%, see SOC median cycle life of battery is larger, but in effect after 500 cycles of delta SOC decline rate is also great.           


Saxena Saurabh et al. Based on the above research results, a life model of LCO/C lithium ion battery is established, and the normal capacity of the battery is shown in the above formula. Among them, EFC is equivalent to the full cycle, A is a power factor, B is a power exponent, and NDC is the normal capacity of Li ion battery. Numerical and B in different SOC and SOC A are shown in the following table           

 

The model is very consistent with the actual test results, because the value of B is almost the same under different conditions, so the B can be set as a fixed constant 0.453. The corresponding one parameter now also need to solve is different SOC and SOC values of A for SOC on 0%-60% in addition to the range of the cell cycle, cycle in other SOC within the scope of the battery can be used SEI membrane growing failure prediction model, thus the equivalent between the ring and the whole cycle time is positive the proportion of A, there are the value and the relationship between SOC and SOC           

 

The calculated A value into NDC% (conventional capacity) of the formula, we can calculate the condition of battery range and delta SOC in different SOC, the cycle life of battery, after verification, the model of life decline income model and the actual test data are very consistent, so the model can be applied in practice, to provide guidance for the design of lithium ion battery and use and maintenance.           

 

But the model can only predict the remaining battery capacity after 500 cycles, when the battery cycle more than 500 times, the battery capacity decline suddenly accelerated, which might be related with the active material particles and SEI membrane rupture, also need to establish a new model to predict this behavior. At the same time, the 0%-60% battery showed a very low capacity decline rate, the current understanding of the mechanism of the phenomenon is not clear, need further study.


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