What causes lithium ion battery life to decrease?

Mobile phones have become a daily necessities for everyone. Presumably, everyone has an experience. With the increase in the use of mobile phones, the standby time of mobile phones will become shorter and shorter, and the daily demand will be able to meet the needs of use. Two charges will work, until the end, one day two charge can not solve the problem, this is what we often say mobile phone battery is not good, we generally call the lithium-ion battery "life decline". What is the cause of the decline in the life of lithium-ion batteries? Before answering this question, we must first familiarize with a concept, what is the life of a lithium-ion battery?

In general, the number of cycles we pass when the capacity of a lithium ion battery drops to 80 % of its initial capacity during the cycle is defined as the lifetime of a lithium ion battery. The mobile phone is an electronic product that needs to be changed frequently. Therefore, the average battery manufacturer will design the life of the mobile phone lithium-ion battery to be about 500 times. That is to say, if we charge the phone once a day, it will take about a year and a half. Our cell phone battery capacity will drop to about 80 % of the initial capacity, which is why we feel that the phone's power is getting less and less. Of course, this is not to say that everyone should not charge as much as possible, but need to charge scientifically and reasonably. At the end of the article, the editor will give you some tips on how to charge the phone. I hope it will help you.

Discussion on Decline Mechanism of Lithium-ion Battery

Here's why lithium-ion batteries decline during use. First of all, we must be clear that in the interior of lithium ion batteries, in addition to the normal lithium-ion embedding and deembedding positive and negative reactions, there will be many side reactions, such as the formation and growth of SEI membranes, electrolyte decomposition, binder decomposition, positive and negative activity. Substances rupture and other factors, Will cause the capacity of lithium-ion batteries to drop. Although there are many factors that cause the decline and fall of lithium ion batteries, it can be grouped into three major categories: 1) lithium loss, because the lithium ion battery is a closed system, the internal material is constant, and the formation and destruction of the SEI membrane, Negative polar lithium, etc. will consume the only Li resources; 2) The loss of positive polar active substances, which often occur during the use of lithium ion batteries, such as particle fragmentation of positive materials, binder decomposition, and changes in the crystal structure of positive polar materials, all of which will cause some positive polar active substances to lose their ability to insert lithium; 3) The loss of negatively active substances, such as the loss of negatively active substances and the decomposition of binders, will cause some negatively active material particles to lose their conductive connection to the conductive network, making it impossible to insert lithium, resulting in the loss of lithium ion battery capacity.

Christopher R. Birkl of Oxford University in the UK recently proposed a method for detecting lithium-ion batteries using an open-circuit voltage. The open circuit voltage of lithium-ion battery is the potential difference between positive and negative poles, which reflects the thermodynamic properties of lithium-ion battery, so it can provide us with rich information about positive and negative poles. Christopher R. Birkl used button batteries to test and verify the impact of the three modes that caused the decline of lithium ion batteries on the open circuit voltage of the battery. It was found that the model that caused the battery decline could be identified by detecting the open circuit voltage curve of the battery. It can be said that the work of Christopher R. Birkl has made a breakthrough contribution to the management of lithium ion battery systems.

Discussion on Decline Mechanism of Lithium-ion Battery

Christopher R. Birkl made a button battery using electrodes removed from a commercial square battery and simulated three lithium ion battery decay modes: 1) lithium loss; 2) Loss of negative polar active substances; 3) loss of positive polar active substances. In order to ensure the accuracy of the test, all experimental batteries need to be stabilized at 3h in the thermostat first to achieve thermal equilibrium. Two voltages were measured in the test, one of which was the voltage measured during the charging and discharging process. This is also called the false voltage. The false voltage can be used to assist in judging the decline and fall mode of lithium ion batteries. It is the open-circuit voltage of the lithium ion battery that can really determine the decline mode of the lithium ion battery.

Discussion on Decline Mechanism of Lithium-ion Battery

First, ChristophR.Birkl calculated the theoretical capacity of the button cell based on the area of the button cell, and then simulated the lithium ion loss by varying the lithium stripping of the positive pole piece by cutting the negative electrode piece. The loss of the negative active material was simulated, and the positive electrode active material loss was simulated by cutting the positive electrode tab. In order to analyze the test results, ChristophR.Birkl used a histogram to create a physical model, as shown in the above figure, where the left side is the negative SoC state, the right side is the positive SoC state, and the upper model is the normal battery model. It can be seen from the figure that in the normal battery design, the capacity of the negative electrode is generally slightly higher, which is generally called positive and negative redundancy, and proper redundancy can ensure the cycle performance of the lithium ion battery, and can also be in the lithium ion. When the battery is overcharged, it can hold enough lithium to ensure that lithium does not precipitate and ensure the safety of the battery.

In this article, we mainly introduce the possible causes of the decline of lithium ion batteries, and Christopher R. Birkl's buckling analog batteries based on these possible factors, simulating: 1) lithium loss; 2) loss of positive polar active substances; 3) Negative active substance loss, a brief introduction to the physical model of the lithium ion battery established by Christopher R. Birkl. In the next article, we will introduce how to use this physical model to analyze the different factors that cause the decline of lithium ion batteries. The impact of open circuit voltage on lithium ion batteries.

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