Isolating membrane and lithium ion secondary battery

Abstract

The invention provides an isolating membrane and a lithium ion secondary battery. The isolating membrane comprises a microporous membrane with micropores and a coating arranged on the surface of the microporous membrane, wherein the coating comprises polymer particles and binder particles, the polymer particles are of empty shell structures, each empty shell structure comprises a shell and a cavity formed inside the shell, nanopores communicated with the cavity are distributed on the outer surface of the shell, and the diameters of the polymer particles are more than the bore diameter of the micropore of the microporous membrane; the diameters of the binder particles are more than the bore diameter of the micropore of the microporous membrane; the lithium ion secondary battery comprises a positive electrode piece, a negative electrode piece, the isolating membrane interlaid between the positive electrode piece and the negative electrode piece, and electrolyte. The isolating membrane has high absorption amount, high ionic electrical conductivity and low heat shrinkage, and the lithium ion secondary battery has good-normal temperature cycle performance, low-temperature discharge performance, rate capability and safety performance.

Description

technical field [0001] The invention relates to the technical field of batteries, in particular to a separator and a lithium ion secondary battery. Background technique [0002] Since the commercialization of lithium-ion secondary batteries, they have been widely used as power sources for various mobile devices due to their high energy density, high operating voltage, and no memory effect. With the large-scale application of lithium-ion secondary batteries, their cycle life and safety issues have become increasingly prominent. [0003] The main components of a lithium-ion secondary battery include a positive pole piece, a negative pole piece, a separator, and an electrolyte. The separator is inserted between the positive pole piece and the negative pole piece in turn. Its main functions are: (1) Physically isolate the positive pole piece and the negative pole piece of the lithium-ion secondary battery to prevent internal short circuit; (2) Ensure the uniformity of lithium i...

AI Technical Summary

Problems solved by technology

[0004] At present, most of the separators used in lithium-ion secondary batteries are polyolefin films, such as polyethylene film (PE), polypropylene film (PP) or polypropylene / polyethylene / polypropylene composite film (PP / PE / PP), When the lithium-ion secondary battery is abused, such as overcharge, thermal shock or puncture, the temperature of the lithium-ion secondary battery will generally reach above 90°C. Once the internal temperature of the lithium-ion secondary battery exceeds 90°C, the traditional PE film, The PP film will have a large shrinkage, resulting in a short circuit between the positive electrode and the negative electrode, generating more heat, making the lithium-ion secondary battery easy to catch fire or even explode.

In addition, the surface tension of the polyolefin film is very low, and the wetting ability and liquid absorption ability of the carbonate electrolyte used in the lithium-ion secondary battery are poor, which cannot meet the requirements of the long cycle life of the lithium-ion secondary battery.

[0005] In response to this situation, the existing practice is to coat a layer of ceramic layer on the separator to reduce heat shrinkage, prevent positive and negative short circuit and improve the wetting ability of the separator to the electrolyte, but the main material of the ceramic layer is generally alumina Ceramic particles with very high hardness will increase the loss of the coating machine and the cutting machine, and increase the production cost, and its liquid retention performance for the electrolyte is also limited, which cannot meet the long cycle life of lithium-ion secondary batteries. requirements, and did not achieve a good suppression effect on abuses such as overcharging

The reason is that when the lithium-ion secondary battery is abused, although the ceramic layer can reduce the thermal shrinkage of the separator, it cannot prevent the temperature of the lithium-ion secondary battery from continuing to rise until the separator melts, and the integrity of the ceramic layer The resistance will also be destroyed, and the positive and negative electrodes will be further short-circuited, causing the lithium-ion secondary battery to catch fire or even explode.

In addition, due to the solid structure of the ceramic particles, the liquid retention capacity of the ceramic layer is limited

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