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The Depth Resolution Comb Attenuation Mechanism Of Lithium Ion Battery

- Nov 19, 2018 -

Lithium battery is the most key, electric cars is also accounted for the highest cost components, can accurately predict and evaluate the attenuation degree of battery life more and more important. Accurate evaluation on the one hand, can improve the vehicle performance and the life of a user experience, on the other hand how optimal allocation proportion of spare parts in business, computing assets, the salvage value also need battery life attenuation analysis as a reference. The current research on lithium battery attenuation usually from three dimensions to analyze, first of all, from the Angle of the electrochemical reaction inside the battery how to analyze the attenuation process of evolution. The second is to different working condition of the battery test in the laboratory, through to the battery voltage, resistance thereof to analyze the characteristics of change. And by collecting a great deal of data on vehicle operation, using machine learning techniques to analysis.

I think had a similar case in the field of natural language processing, in the original language linguists occupied the main position in the process of research, at that time is generally accepted that if need to make computer language translation or language understanding, the premise is to make the computer understand the meaning of the sentence. So the researchers put the research emphasis on the grammatical analysis, hope to make the computer through the syntax analysis tree decomposition algorithm language comprehension. This way and try to understand by the electrochemical reaction mechanism to assess the thinking of battery life is similar. And because the model complexity is high, the random factors such as large interference reason cannot get the ideal effect.

After 2000 Google invest large amounts of energy in the field of language processing, and adopted a statistical analysis of the technical route of replacing the language rule analysis of route. Computer not understand language intention, but through the network on a large number of sample statistics to form a set of mathematical model related to context (i.e. word may have multiple meanings, through statistical analysis to determine the meaning of each context in the sentence the likelihood probability), finally achieved breakthrough progress.

With the rise of the electric car market share, using machine learning technique route may be able to better solve the problem of life assessment. Of course this is not to say the battery electrochemistry reaction mechanism is not necessary, instead to understand attenuation mechanism of battery and battery external characteristic changes and machine learning is to build mathematical model and implementation. So this paper tries to comb attenuation mechanism of lithium ion batteries, which can better understand and imagine the battery. Especially when the data analysis results and assume that there are differences, if the battery reaction mechanism has certain concepts, then put forward a new hypothesis can be more accurate.

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1. The working principle of lithium-ion batteries

1) the positive and negative

The positive is the anode material of lithium-ion batteries, such as the LFP, sliding) coating on aluminum foil (fluid), the cathode is the anode materials (such as graphite, LTO) coating on copper foil (fluid). Usually battery is named according to the anode material, so that the ternary batteries or lithium iron phosphate batteries; And titanate LTO anode materials is in the lithium battery, so it is named after the cathode material special case of the battery. When reading foreign literature found in this paper, often called the Anode material of Cathode (Cathode), the Anode materials is called the Anode (Anode), the beginning is not very understanding, because we usually think, electrode is Cathode reduction reaction, oxidation reaction of electrode is Anode; The switch in the discharge and charge of the battery have been extremely Yin and Yang in the process of changing. Later slowly a little want to understand, this definition should be refers to the external conditions of the influence of the energy situation, so in order to discharge under the reaction conditions to determine the anode of the battery.

2) the diaphragm

There is a layer of the diaphragm between the cathode (Separator), that is negative segregation, prevent electronic through, at the same time can make the lithium ions pass.

3) electrolyte

Electrolyte in the play the role of conductive lithium ion batteries. In the process of battery discharge, Li + from the cathode through the diaphragm to the anode, electrons from the cathode forms through an external circuit back to the anode current. The opposite battery charging process. Will, in the process of the battery into the electrolyte and electrode materials (mainly cathode) interface reaction, consumes part of Li +, and forming a passivation layer in the surface of electrode materials, known as "a Solid electrolyte interface membrane" SEI (Solid electrolyte interface). SEI is electronic insulators, but is the conductor of Li +. The formation of a stable SEI for Li + embedding and out freely.

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2. Define the battery attenuation

Battery attenuation can be divided into two aspects, on the one hand is performance, on the other hand is security.

1) performance attenuation

After some time the use of electric cars in range will be decreased, the acceleration attenuation can be felt. This major can be from the attenuation of capacity, internal resistance increases, and the increase of battery self-discharge several aspects to analyze.

2) security attenuation

The safety of attenuation is relatively more difficult than perceived. Batteries are a mechanical deformation, or is likely to occur in the increasing probability of short circuit, and the risk of leakage.

What effect so it follows that we can find the reduced capacity, internal resistance increase caused by what factors, battery deformation process, and the factor that lead to short circuit occurred in such a problem to understand the attenuation process of the battery.

In order to facilitate understanding, I suddenly thought of a metaphor: we can compare the anode to "factory", the cathode compared to "the apartment", Li + compared to "staff". Then discharge is employees from the apartment to the energy release of the factory, the charging process employees go back to the apartment is rest supplement energy. From the metaphor one can imagine whether factory jobs, or the disrepair of the apartment, and the loss of employees, can eventually lead to the decay of the whole.