Separators lithium-ion batteries

The process for making lithium-ion battery separators can be broadly divided into dry - and weH processes. Both processes usually employ one or more orientation steps to impart porosity and/or increase tensile strength. The dry process involves melting a polyolefin resin, extruding it into a film, thermally... 

Table 2. Major Manufacturers of Lithium-Ion Battery Separators along with Their Typical Products ...

The general requirements for lithium-ion battery separators are given below. 

Porosity. It is implicit in the permeability requirement typically lithium-ion battery separators have a porosity of 40%. Control of porosity is very important for battery separators. Specification of percent porosity is commonly an integral part of separator acceptance criteria. 

Table 5. General Requirements for Lithium-ion Battery Separator ...

Separators in lithium ion batteries must separate positive electrodes and negative electrodes to prevent short circuits, and must allow passage of electrolytes or ions. Porous films and nonwoven fabrics of resins are known separators. The lithium ion battery separators are also required to exhibit stable properties at high temperatures such as in charging, and therefore high heat resistance is desired (21). 

Preferably, the lithium ion battery separators range in average fiber diameter from 1-3 p, and in basis weight from 10-20 g m-2 The average fiber diameter and basis weight are substantially the same before and after the pressing. The lithium ion battery separator desirably has a porosity of 40 to 50%, and a thickness of 20-45 p. A lithium ion battery separator with this porosity value provides a low internal resistance and does not pass electrode substances to prevent short circuits. The thickness in the above range is suitable for the separator to be applied to small sized lithium ion batteries (21). 

Costa, C.M., Sencadas, V., Rocha, I.G., Silva, M.M., Lanceros-Mndez, S., 2013. Evaluation of the main processing parameters influencing the performance of polyfvlnylidene fluoride-trifluoroethylene) lithium-ion battery separators. J. Solid State Electrochem. 17,861-870. 

During the manufacture of many polymer-containing materials, and particularly solid state lithium ion battery separators and electrodes, it is desirable to include plasticizers so that the components will be rendered porous after the plasticizer was removed. Many porous membranes and other similar porous rrraterials are produced using this method. Plasticizer is continuously reused in such processes. Plasticizers are frequently removed by extraction with suitable solvents but they rrray evaporate under low heat and low pressure conditions as described in the preserrt inverrtioa Plasticizer is removed by conductive heat transfer, forced air convection, or radiative heating, all conpled with application of the vacuum. 

Zhang J, Kong Q, Liu Z, Pang S, Yue L, Yao J, et al. A highly safe and inflame retarding aramid lithium ion battery separator by a papermaking process. Solid State Ionics 2013 245-246 49-55. 

Table 20.2 Major manufacturers of lithium-ion battery separators along with their typical products...

The separator should form a good interface with the electrodes to provide sufficient electrolyte flow. In addition to the above properties, the separator must be essentially free of any type of defects (pinholes, gels, wrinkles, contaminants, etc.). All of the above properties have to be optimized before a membrane qualifies as a separator for a Li-Ion battery. The general requirements for Lithium-Ion battery separators are summarized in Table 20.5. 

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