How to deal with and handle square lithium ion battery problems


  Author :Iflowpower – Portable Power Station Supplier

1. Square Battery Basic Structure A typical square lithium ion battery, tight composition components include: top cover, housing, positive electrode plate, a negative electrode plate, diaphragm composed of laminated, insulator, safety assembly, etc. Among them, two of the red circles are safety structures, NSD acupuncture safety devices; OSD overcharge protection.

Acupuncture safety protection device (NSD, NAILSAFETYDEVICE). This is the outermost surface of the core plus metal layer, such as copper sheets. When the acupuncture occurs, local large currents in the acupuncture position quickly decrease the current of the unit area in the large area of ​​the copper flakes, which can be partially overheated by the needle acupuncture position, and slow down the battery thermal out of control.

Overcharge safety protection device (OSD, overchargesafety DEVICE), current security design can see on many batteries. Generally, a metal sheet is used in conjunction with the FUSE, and the FUSE can be designed to the positive electrode current, and the pressure inside the battery has caused the OSD to trigger the internal short circuit, and the instantaneous high current, so that the FUSE is blown, thereby cutting off the internal current circuit of the battery. The housing is generally a steel shell or aluminum shell, and the aluminum shell gradually became mainstream with the driving process of the market's pursuit of energy density and the progress of the processing process.

2. Square Battery Features Square Battery is a kind of power-promoting lithium-ion battery in China. In 2016, the data showed that domestic cylinders, soft bags, square lithium ion batteries were 13.

92 g wh, 21.64GWH, 28.14GWH, accounting for 21.

85%, 33.97%, 44.17%, respectively.

Square batteries have been re-acquired. Advantage, high battery pack reliability; high system energy efficiency; relative weight, high energy density; more simple structure, relatively convenient, is currently increasing the energy density by increasing the unit capacity; The system is relatively simple, making it possible to monitor the one by one of the monomers; the other benefits of the system simply brought the stability relatively good. Disadvantages, because the square lithium ion battery can be customized according to the size of the product, there are thousands of models on the market, and because there are too many models, the process is difficult to unify; the level of processing is not high, the monomer difference Larger, in large-scale use, there is a problem that the system life is much lower than the single life life.

Speaking here, I can't mention the July 2017, the national recommendation standard "GB / T34013-2017 electric vehicle" GB / T34013-2017, "Dimensional Size", for the square battery, 8 series, for square batteries, 8 series Size, as shown below and below. Personally, guide the size of the battery, may not have a particularly distinctive effect in a short period of time, and even some people think that this time gives the commanding opinion, it will bind the industry development, and change the product size, the battery is machined, not only It is only the problem of tooling molds, which affects very much. But as a recommendation standard, as long as it is possible to prepare a new processing force and a manufacturer of the production line, it will inevitably develop to the series of specifications to develop the specifications.

The consistency of the battery and modules is the premise of truly realizing the use of the ladder. As for the technical route, there may be across the future, in fact, it does not affect the effort to move forward to visible targets before crossing. 3, it is necessary to see two forms before the manufacturer, the domestic important manufacturer information is here.

Source: Dynamic Lithium Ion Battery Use Branch Research Department to organize foreign countries Samsung SDI, the positive electrode material is tightly adopted NCA and NCM, square aluminum shell. Famous case BMW I3. Square battery monomer displayed by Samsung official website.

Products include high energy BEV (pure electric) 60AH, 94AH battery; PHEV (plug-in mixed electric vehicle) 26AH, 37AH battery (26ah will gradually replaced by 37ah); HEV (mixed electric vehicle) 5.2ah, 5.9ah battery; High power battery (4.

0ah, 11ah), a total of 4 series. 4. Typical square battery module The following figure is Mitsubishi 2011 I-MIEV battery module, PCB board collects Cell voltage, temperature, and both ends through bolts.

CELL is the most common BUSBAR and bolt connection method. Next is the 2012my Toyota Pres Phev battery module, using the harness (see this harness to see this harness, it feels very troublesome, there is hidden dangers) to collect Cell information, but also the connection method of bolts, However, some of the new orange is protected. Below is the battery module of 2014my Volkswagen Jetta HEV, and fasten the module by two pieces of the side, and the outer side of the end plate is insulated.

Volkswagen EGOLF2015MY battery module, the design of the end plate is relatively rich, and the weight loss meets the structural strength demand, but also reaches the demand for assembly, using the PCB board to collect CELL information, the module should leave a low pressure joint (now using The module in this way is more and more). The picture below is the design concept diagram of Audi 2014, the design concept of the matching liquid cold board, from the explosion map, some internal structures that can be seen above. BMW I3, using Samsung SDI square battery.

There are 8 modules in the battery pack. Each module has 12 batches. Total 96 cells are connected in series, and the 183km battery end uses a 94AH battery, as shown below.

(Description, the picture below is not the latest version of the legend, the video flowing on the Internet shows that the latest version of the Pack box has been different from the previous version. Aluminum welding mode housing, four-angle has an installed via fixed to the PACK box, the structure is simple, which is advantageous for automation manufacturing. Square cells make capacity, relative cylindrical cells, and less restrictions in the process of lifting capacity.

However, with the new volume of the monomer, there have been some problems, such as the surface of the side, the surface is severe, and the heat dissipation is difficult and the unevenness is increased. 5, square battery typical problems and response to side bulging problems There is a certain pressure in the internal battery in the charging and discharge process (0.3 ~ 0.

6 MPa), under the same pressure, the larger the power area, the battery The more severe the deformation of the shell wall. The tight source caused by the expansion of the battery is formed in the process of forming the SEI. When the gas is formed, the air pressure in the battery increases.

Because the square battery planar structure is poor, the housing deformation is caused; the electrode material lattice parameters change, resulting The electrode expansion, the electrode expansion force is used in the housing, resulting in deformation of the battery housing; when high temperature storage, a small amount of electro-hydraulic analysis and increased temperature effect gas pressure, resulting in deformation of the battery housing. The housing expansion caused by the above three protocols is the most important origin. The bulk problem of square batteries is a common problem, especially the large-capacity square lithium-ion battery is more serious.

The battery bulge can cause new internal resistance of the battery, and the local electro-hydraulic depletion or even housing is broken, which seriously affects the safety of the battery. Circular life. Zhang Chao is given by people, using small structures, enhances the strength of the housing; optimizes two angles of arrangement, and handles square battery bulge problems.

Enhance the strength of the housing, design the original planar housing into enhanced structure, and detect the effect of the housing enhanced structure design in such a manner of pressing the housing, in accordance with the different fixed mode (fixed longitudinal direction and fixed width direction), Division. The use of enhanced structures can be observed. Taking the width fixed situation as an example, under 0.

3 MPa pressure, the amount of deformation of the enhanced structure is 3.2mm, and the amount of housing deformation without the reinforcing structure reaches 4.1 mm, and the deformation is reduced by 20%.

Width fixed conditions: Pressure under length fixation: Optimize the electrical cell arrangement in the module, the researchers compare two arrangements, as shown below, the amount of deformation is as shown in the table below. Comparison, it is found that the thickness direction of the arrangement II is divided into the arrangement of the arrangement. Large square battery heat dissipation performance As the size of the monomer, the heat of the heat generation of the battery is increasingly long, the medium is conducted, and the interface is increasing, so that heat dissipation is difficult, and in monomers The problem of uneven heat distribution is getting cleared.

Wu Weixiong et al. Conducted a study, and the trial was used to use a square lithium-ion battery with 3.2V / 12AH.

The base is shown in Table 1. The battery charger device is the Xinwei CT-3001W-50V120Antf. The ambient temperature is 31 ° C, the heat dissipation is air cooling, and the temperature change of the battery is recorded with a temperature inspection instrument.

Test step: 1) Pressure, charge the battery to the battery with 12A current to the charging cutoff voltage 3.65V stop current 1.8a; 2) She hold, then put it on hold for 1 hour to stabilize the battery; 3) Constant current discharge, discharge at different magnification To the discharge cutoff voltage 2V.

Among them, the discharge magnification is set to 1C, 2C, 3C, 4C, 5C, 6C, respectively. As shown in the figure below, the temperature changes in the surface of the battery at different discharge ratins, it can be seen that the temperature is increasing, the temperature is increasing, and the highest temperature corresponding to each discharge rate is 38.1, 48.

3, 56.7, respectively. 64.

4, 72.2, 76.9 ° C.

When the 3C magnification is discharged, the maximum temperature has exceeded 50 ° C. When the 6C, the temperature reached 76.9 ° C and more than 50 ° C for 470 s, accounting for two-thirds of the entire discharge process, which is very disadvantageous about battery safety continues.

The phase change material is used as the thermally conductive medium, attached to the surface of the monomer battery, and the heat dissipation effect is greatly improved. Comparison of temperature rise after application of the thermally conductive material is shown in the figure below: In addition, there is also a way, combining the thermally conductive material with water cooling, allowing the water-cooled system to pass the heat of the heat conductive material to the outside of the system, and the form is as follows: lithium Ion battery system, related to hot loss of control, the most ideal is able to test the parameters of each cell (the most basic temperature, voltage, current, etc.), such, even if there is no new type of low-cost function.

The sensor will become possible, and the warning and disposal of thermal out of control will become possible. There are fewer in the system, which should be one of the important competitiveness of square batteries.

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