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Sep 12, 2019   Pageview:164

Lithium ion batteries after completion of production, producing process, the winding or laminated means the positive and negative pole piece and diaphragm assembly manufacturing form basic batteries.Then, generally for thermal plastic batteries.This paper mainly introduces the purpose of the extrusion shaping process and the key points of process control.

The purpose of, process

No matter in the winding or Z fold, must exert a certain tension on the diaphragm, in order to ensure positive plate, diaphragm, neat degree between the cathode piece, however, the technological process of tension can make the diaphragm in the direction of tape elongated, the diaphragm shrinkage is very big, at the direction of tape will make serious extrusion sheet diaphragm, which leads to batteries after assembly process, especially the coiling process, deformation of batteries, batteries after deformation is not only appearance smoothness is poor, also exist inside the diaphragm defects such as fold, as shown in figure 1 and figure 2, which leads to low capacity, fast cycle performance is poor and self-discharge of quality problem, especially the winding of the thicker batteries, especially after the winding deformation problem.In addition, the thickness of loose state of batteries consistency is bad, will affect the batteries into the shell process, increase the difficulty of the process into the shell, and even lead to cell damage into the shell.

Therefore, the main purpose of the batteries, hot pressing shaping include:

(1) improve lithium ion battery flatness, thickness of the batteries meet requirements and have high consistency;

(2) to eliminate the diaphragm fold, out of the internal air batteries, make diaphragm and anode plate is tightly stick together, shortening the distance between the lithium ion diffusion, reduce the battery internal resistance.

Second, the technological process

In order to make the lithium-ion battery batteries can recover after plastic flat and avoid retraction.Batteries hot pressing shaping process is as follows: put the winding or laminated good batteries on the template, set the pressure cylinder pressure and temperature, the templates and template under certain pressure and temperature is up and down make batteries to finalize the design, to achieve the thickness of the batteries is consistent, reduce cell elasticity, lower core qualified rate and confirmed

The consistency of the finished product the thickness of the batteries.

For square cells, hot pressing shaping device as shown in figure 3, from top to bottom template is flat, smooth flat clamping batteries under pressure.For the cylindrical battery, hot pressing shaping device on the base to produce two cylinder relative to one another, the two cylinder piston rod end with two semicircle model of cylindrical tank, two semicircle model equals the radius of cylindrical tank and is equal to or less than the default volume core radius.Using manipulator or fixture clamping roll core is placed in the center of the two semicircle model, the mould clamping the two cylinder to drive two semicircle relative to one another, making two semicircle die extrusion of roll core and the winding plastic to preset size, to allow into the matching of the enclosure.

Generally, when in batteries, plastic, dielectric withstand voltage test was carried out on the batteries at the same time, the existence of micro short circuit detection technology for batteries.If batteries inside the presence of tiny metal foreign body particles, was down state in batteries, batteries, diaphragm punctured, it is easy to detect the micro short circuit nonconforming product.About batteries insulation withstand voltage test, sorting before an article:The lithium battery basic knowledge of batteries insulation withstand voltage test (click here to read).

Three, the key points of technology

Batteries, hot pressing shaping the main process parameters have pressurized pressure, pressure time and temperature of the template.Under appropriate process parameters, the thick batteries almost non-existent internal air, the diaphragm and the pole piece close together, loose batteries can become lumps.But, for the use of ceramic membrane in recent years, because of the ceramic layer exists, the diaphragm to pole piece together to form this kind of state.In the process to determine the test, the test items include membrane permeability, thickness change;The thickness of the batteries if they meet the requirements of the shell;If pole piece break, etc.

Battery diaphragm as the core component of the battery, give play to the isolation are negative electrons, while allowing lithium ion between the poles of reciprocating through the key role of the microporous structure of the diaphragm is the importance of these ions is shuttling between the cathode channel, its permeability will directly affect the performance of the battery diaphragm permeability refers to the diaphragm in a certain amount of time through the amount of gas under pressure.If the membrane permeability is bad, will affect the lithium ion between is negative transfer, which in turn influence lithium battery of charging and discharging.Test process is: the fixed battery diaphragm, applying pressure on one side of the diaphragm, the barometric pressure drop and the time of measurement, detection of the diaphragm porosity, the shorter the time used, permeability is, the better.In the process of hot pressing, the diaphragm may be severely compressed, diaphragm thickness change is big, cause pore blockage, visualizing the diaphragm will become transparent color, this kind of situation shows that thermal plastic overrun, the action of the batteries will affect the lithium ion transport.Winding batteries as shown in figure 2, if the plate is brittle, batteries, bending in thermal plastic prone to falling powder or rupture, which leads to limited electronic transmission, increase the battery internal resistance.Therefore, batteries, thermal plastic must also avoid this kind of circumstance happening.These two aspects for hot pressing shaping pressure as small as possible, the shorter the time, the better.And on the other hand, thermal plastic and must make batteries to finalize the design, the thickness of the batteries meet the technological requirements, batteries, elasticity is reduced, and ensure the consistency of the thickness of the finished batteries.Therefore, pressure, time and temperature and so on need to optimize process parameters.

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