First, after the lithium-ion battery production process, after the positive and negative pole roller pressing roll is then placed in the battery case, the lithium ion battery electrical core group must be baking drying.. It is well known that the effect of moisture on the performance of the lithium ion battery is the largest, and the moisture inside the lithium ion battery cell is removed before the assembly work, so as not to affect the quality of the lithium-ion battery.
. Among the negative pressure environments where the battery is baked, the core is placed on the outer body of the baking box, and drying drying by an inert gas into an inert gas..
However, during the actual baking process, since the temperature and moisture change process inside the battery cell is not visible, the blindness of the internal environment and baking time is caused, which directly affects the quality of the battery. This effect is the battery core. The process and the final battery baking can’t be kept.
Therefore, the temperature change and moisture evaporation of the electrical core when the battery is baking is very necessary.. The end of the end is only the opening of the electrolytic solution, and the moisture is almost evaporated by the upper end of the battery.
The battery core is exposed to the convection transmission of heat transfer radiation and inert gas, heat transfer to the battery process, one aspect On the other hand, the battery temperature is used to evaporate free water in the battery.. Its evaporation position is schematic and a model battery size is shown in Figure 1.
Figure 1 Distake in the battery baked 2, the core baking heat conduction theory analysis In the baking process, the heat source has a certain gap between the upper end of the baking box, the battery and the oven, for ensuring the battery. Baking temperature, also facilitating evaporation of moisture except through the gap. The temperature change at the time of the battery can be calculated by the Fourier thermal conductive law: ρG is the average density of positive and negative pole slice inside the battery; CP is a battery comparison heat capacity; T is the battery core heat conduction Thermal efficiency; x, y, z is the spatial coordinate function; L is a water-resistant latent heat inside the cell; m is the moisture content of the electrical core.
. The boundary condition of the battery is set to: TR, TS, Tair is a heat source in the baking box, and the surface temperature of the battery, the internal ambient temperature of the baking box; DW is the moisture diffusion coefficient of the battery cell; ρW Liquid water density. The heat conduction coefficient is divided into two parts, HR is the heat radiation heat conduction coefficient, and HC is the intensity of flow heat conduction coefficient in the oven, in which σ is Stephen-Bolzman constant; HC = 0.
5; εp and εr are battery cells and heat sources, respectively The thermal radiation coefficient; the FSP is the shape coefficient of two parallel splints outside the oven battery, and its calculation formula is: the distance between the LSP is between the heat source and the surface of the oven; the ASP and BSP are the length and width of the battery. The factors are set by the above results. In order to facilitate the analysis, the temperature and moisture change of the cell is described, and the cells are divided into surface, middle and bottom three parts, and the surface part of the battery is nearest.
. The calculation can obtain temperature changes in three parts of different time cells, as shown in Figure 2. Figure 2 The results of the core internal temperature and time change graph show: When the start of the baking begins, the measurement of each part of the battery is slowly elevated, the surface temperature is raised, the bottom is slow, baked After 95min, the part of the battery gradually reaches the highest temperature, and the internal temperature of the oven is consistent.
. Third, the electro-steam evaporation mechanism study the evaporation of the moisture, the effect of concentration gradients on the dryness is not only on the surface, but also has the same effect on the interior..
The water evaporation diffusion process for the battery can be calculated in accordance with the law of Phke: D is: D is the moisture effective diffusion coefficient inside the battery, and the simultaneous containment of moisture and water vapor diffusion.. Since the electrical core moisture content is minimal, the temperature during the baking process does not cause the attribute change of the battery, so the compression amount and physical chemical changes of the battery core material during moisture can be ignored.
. The setting boundary condition is: in the formula, MAIR and M0 are the moisture content of the baking box inside and the battery in the initial conditions; HV is the transfer coefficient of the moisture inside the battery core to the oven environment..
The moisture evaporation process inside the battery can be analyzed by simplifying two-dimensional simplified simplified two-dimensional simplified simplified, but the model, the primary boundary condition and material properties cannot be completed, which is not possible to complete the actual situation of the model, the primary boundary conditions and material properties of the Fluent. Be conducive to function. UFD uses the Define macro, written by C language, the temperature and moisture transfer function of the battery core and the water transfer function and the boundary condition are programmed, and the writable UFD is loaded into the fluent.
. The sequential process is shown in Figure 3. Figure 3 Baking Cod Water Split Evaporation Fluent Simulation Flow Distament Using Fluent Simulation Software Simulation analysis of moisture evaporation speed inside the designated size battery, as shown in Figure 4.
Figure 4 Different time cells internal moisture evaporation speed simulation results are calculated, the amount of water content of 3 different parts of the battery during the battery bake, as shown in Figure 5, assuming that the battery is baked before baking, each cross The water content of the longitudinal section is consistent. The results of the water content and time change graph in the electrical core indicate that the water surface water evaporation rate is very fast at the beginning of the baking, and the water content is slowly reduced, and the intermediate portion of the battery starts 20 min. The left and right evaporation speed reaches the maximum, and the bottom of the battery is not obvious at the beginning of the baking, and the moisture content is reduced in the left and right moisture content of the bake.
. The numerical calculation parameter value of the battery bake process is shown in Table 1. Table 1 The battery bake process calculation parameter value 4, the conclusion The vacuum baking of the battery before the liquid is very important, the temperature change and moisture content inside the battery can pass the Fourier thermal conduction law and the Law of Phke Research analysis is obtained, and the research on the actual baking process of the battery and the baking process have guided significance.
. For the designated size lithium-ion battery cell, temperature change is evenly elevated from the electrical core surface to the bottom layer, and the entire cell is reached at 95min, and the electric wire is different, the battery is different, and the baking begins The mid-core water removal is the fastest, and the water content in the late stage is smooth but does not reach the designated low water content, which is the cause of the electrical core and the bottom of the bottom from the surface, and the bottom of the battery is bake in the middle and late water. Remove the maximum, the entire battery is reached in the entire battery.