According to the requirements of group friends, talk about the understanding of lithium battery quick charging:

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Gunakan rajah ini untuk menggambarkan proses pengecasan bateri. Abscissa ialah masa dan ordinat ialah voltan. Pada peringkat awal pengecasan bateri litium, akan terdapat proses pra-cas semasa kecil, iaitu pra-cas CC, yang bertujuan untuk menstabilkan bahan anod dan katod. Selepas itu, bateri boleh dilaraskan kepada Charge dengan arus tinggi iaitu CC Fast Charge, selepas bateri stabil. Akhirnya, ia memasuki mod pengecasan voltan malar (CV). Untuk bateri litium, sistem memulakan mod pengecasan voltan malar apabila voltan mencapai 4.2V, dan arus pengecasan secara beransur-ansur berkurangan sehingga pengecasan tamat apabila voltan lebih rendah daripada nilai tertentu.

Semasa keseluruhan proses, terdapat arus pengecasan standard yang berbeza untuk bateri yang berbeza. Sebagai contoh, untuk produk 3C, arus pengecasan standard biasanya 0.1C-0.5C, manakala untuk bateri kuasa tinggi, pengecasan standard biasanya 1C. Arus pengecasan rendah juga dipertimbangkan untuk keselamatan bateri. Jadi, katakan pada masa biasa cas pantas, ia adalah untuk menunjuk kepada beberapa kali lebih tinggi daripada arus cas standard kepada berpuluh kali ganda.

Some people say that charging lithium batteries is like pouring beer, fast and filling beer fast, but with a lot of foam. It’s slow, it’s slow, but it’s a lot of beer, it’s solid. Fast charging not only saves charging time, but also damages the battery itself. Due to the polarization phenomenon in the battery, the maximum charging current it can accept will decrease with the increase of the charge and discharge cycle. When the continuous charging and the charging current is large, the ion concentration at the electrode increases and the polarization intensifies, and the battery terminal voltage cannot directly correspond to the charge/energy in a linear proportion. At the same time, high current charging, the increase of internal resistance will lead to intensified Joule heating effect (Q=I2Rt), bringing side reactions, such as the reaction decomposition of electrolyte, gas production and a series of problems, the risk factor increases suddenly, has an impact on battery safety, the life of non-power battery will be greatly shortened.

01

Bahan anod

The rapid charging process of lithium battery is the rapid migration and embedding of Li+ in the anode material. The particle size of the cathode material can affect the response time and diffusion path of ions in the electrochemical process of the battery. According to studies, the diffusion coefficient of lithium ions increases with the decrease of the grain size of the material. However, with the decrease of material particle size, there will be serious agglomeration of particles in the production of pulping, resulting in uneven dispersion. At the same time, nanoparticles will reduce the compaction density of the electrode sheet, and increase the contact area with the electrolyte in the process of charge and discharge side reaction, affecting the performance of the battery.

Kaedah yang lebih dipercayai ialah mengubah suai bahan elektrod positif dengan salutan. Sebagai contoh, kekonduksian LFP itu sendiri tidak begitu baik. Menyalut permukaan LFP dengan bahan karbon atau bahan lain boleh meningkatkan kekonduksiannya, yang kondusif untuk meningkatkan prestasi pengecasan pantas bateri.

02

Anode materials

Fast charging of lithium battery means that lithium ions can quickly come out and “swim” to the negative electrode, which requires the cathode material to have the ability of fast embedding lithium. The anode materials used for rapid charge of lithium battery include carbon material, lithium titanate and some other new materials.

Untuk bahan karbon, ion litium lebih disukai dibenamkan ke dalam grafit di bawah keadaan pengecasan konvensional kerana potensi pembenaman litium adalah serupa dengan pemendakan litium. Walau bagaimanapun, di bawah keadaan pengecasan pantas atau suhu rendah, ion litium boleh memendakan pada permukaan dan membentuk litium dendrit. Apabila litium dendrit menusuk SEI, kehilangan sekunder Li+ telah berlaku dan kapasiti bateri berkurangan. Apabila logam litium mencapai tahap tertentu, ia akan berkembang dari elektrod negatif ke diafragma, menyebabkan risiko litar pintas bateri.

As for LTO, it belongs to the “zero strain” oxygen-containing anode material, which does not produce SEI during battery operation, and has stronger binding ability with lithium ion, which can meet the requirements of fast charge and release. At the same time, because SEI cannot be formed, the anode material will directly contact with the electrolyte, which promotes the occurrence of side reactions. The problem of LTO battery gas generation cannot be solved, and can only be alleviated by surface modification.

03

Electrode liquid

As mentioned above, in the process of fast charging, due to the inconsistency of lithium ion migration rate and electron transfer rate, the battery will have a large polarization. So in order to minimize the negative reaction caused by battery polarization, the following three points are needed to develop the electrolyte: 1, high dissociation electrolyte salt; 2, solvent composite – lower viscosity; 3, interface control – lower membrane impedance.

04

Hubungan antara teknologi pengeluaran dan pengisian cepat

Before, the requirements and influences of fast filling were analyzed from three key materials, such as positive and negative electrode materials and electrode liquid. The following is the process design that has a relatively large impact. The technological parameters of battery production directly affect the migration resistance of lithium ions in each part of the battery before and after battery activation, so the technological parameters of battery preparation have an important influence on the performance of lithium ion battery.

(1) slurry

For the properties of slurry, on the one hand, it is necessary to keep the conductive agent evenly dispersed. Because the conductive agent is evenly distributed among the particles of the active substance, a more uniform conductive network can be formed between the active substance and the active substance and the collector fluid, which has the function of collecting micro current, reducing the contact resistance, and can improve the movement rate of electrons. On the other hand is to prevent the over-dispersion of conductive agent. In the charging and discharging process, the crystal structure of anode and cathode materials will change, which may cause the peeling off of conductive agent, increase the internal resistance of the battery, and affect the performance.

(2) Extremely partial density

Secara teorinya, bateri pengganda dan bateri berkapasiti tinggi tidak serasi. Apabila ketumpatan polarisasi elektrod positif dan negatif adalah rendah, halaju resapan ion litium boleh ditingkatkan, dan rintangan penghijrahan ion dan elektron dapat dikurangkan. Semakin rendah ketumpatan permukaan, semakin nipis elektrod, dan perubahan struktur elektrod yang disebabkan oleh pemasukan dan pelepasan ion litium yang berterusan dalam cas dan nyahcas juga lebih kecil. Walau bagaimanapun, jika ketumpatan permukaan terlalu rendah, ketumpatan tenaga bateri akan berkurangan dan kos akan meningkat. Oleh itu, ketumpatan permukaan perlu dipertimbangkan secara menyeluruh. Rajah berikut ialah contoh bateri litium kobalt mengecas pada 6C dan menyahcas pada 1C.

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(3) Polar piece coating consistency

Sebelum ini, seorang rakan bertanya, adakah ketidakkonsistenan ketumpatan yang sangat separa akan memberi kesan kepada bateri? Di sini, untuk prestasi pengecasan pantas, yang utama ialah ketekalan plat anod. Jika ketumpatan permukaan negatif tidak seragam, keliangan dalaman bahan hidup akan berbeza-beza selepas bergolek. Perbezaan keliangan akan membawa kepada perbezaan pengagihan arus dalaman, yang akan menjejaskan pembentukan dan prestasi SEI dalam peringkat pembentukan bateri, dan akhirnya menjejaskan prestasi pengecasan pantas bateri.

(4) Ketumpatan pemadatan kepingan tiang

Why do poles need to be compacted? One is to improve the specific energy of the battery, the other is to improve the performance of the battery. The optimum compaction density varies with the electrode material. With the increase of compaction density, the smaller the porosity of electrode sheet, the closer the connection between particles, and the smaller the thickness of electrode sheet under the same surface density, so the migration path of Lithium ions can be reduced. When the compaction density is too large, the infiltration effect of electrolyte is not good, which may destroy the material structure and the distribution of conductive agent, and the later winding problem will occur. Similarly, lithium cobalate battery is charged at 6C and discharged at 1C, and the influence of compaction density on discharge specific capacity is shown as follows:

Gambar

05

Formation aging and others

For carbon negative battery, formation – aging is the key process of lithium battery, which will affect the quality of SEI. The thickness of SEI is not uniform or the structure is unstable, which will affect the quick charging capacity and cycle life of the battery.

In addition to the above several important factors, the production of cell, charge and discharge system will have a great impact on the performance of lithium battery. With the extension of service time, the battery charging rate should be moderately reduced, otherwise the polarization will be aggravated.

kesimpulan

Intipati pengecasan pantas dan nyahcas bateri litium ialah ion litium boleh dinyahbenamkan dengan cepat antara bahan anod dan katod. Sifat bahan, reka bentuk proses dan sistem pengecasan dan nyahcas bateri semuanya mempengaruhi prestasi pengecasan arus tinggi. Kestabilan struktur bahan anod dan anod adalah kondusif untuk proses delitium yang cepat tanpa menyebabkan keruntuhan struktur, ion litium dalam kadar resapan bahan lebih cepat, untuk menahan pengecasan arus tinggi. Disebabkan ketidakpadanan antara kelajuan penghijrahan ion dan kadar pemindahan elektron, polarisasi akan berlaku dalam proses pengecasan dan nyahcas, jadi polarisasi harus diminimumkan untuk mengelakkan pemendakan logam litium dan mengurangkan kapasiti untuk menjejaskan kehidupan.