A secure lithium ion electric core and its making method

Abstract

The utility model relates to a safety lithium-ion cell and a manufacturing method adopting a composite winding structure inside, which is characterized in that a composite diaphragm of at least two different properties is arranged inside the electrical core; wherein, one layer of the composite diaphragm is that microporous film of irradiation-crosslinking PDVF substrate coated on the pole piece; the other layer is that polyolefin microporous film with a shutdown temperature between 120 and 165 degree Centigrade. The chemical gel content formed in the PDVF microporous film after irradiation crosslinking is 25 to 85 percent, the thermal shrinkage rate within 100 - 220 degree Centigrade is less than 5 percent; and the anode uses preferably spinel manganate lithium.

Description

technical field [0001] The invention relates to a lithium ion secondary battery, in particular to a lithium ion electric core with high safety. Background technique [0002] Lithium-ion secondary batteries have the advantages of high working voltage, high energy density, and environmental protection, and are widely used in mobile phones, notebook computers, power tools, electric bicycles and other products. [0003] In the liquid lithium-ion batteries widely used in general, the high-strength polyolefin microporous diaphragm used in the electrolyte has a general ability to absorb liquid and accommodate the electrolyte. In the winding structure, especially in the four There are gaps between the positive and negative electrodes and the diaphragm that are not completely filled with the electrolyte at the rounded corners, resulting in uneven polarization when the cells are formed, insufficient capacity and inconsistent mass production, especially in high-capacity cells. It is m...

AI Technical Summary

Problems solved by technology

However, the polyvinylidene fluoride microporous membrane produced by this method has low strength and cannot meet the requirements of high-efficiency winding production technology. Instead, it adopts a composite laminated structure of positive pole piece, separator, and negative pole piece. to about 50 microns; another disadvantage of this method is that the extraction efficiency is low, the requirements for production safety protection are high, the manufacturing cost is large, and the economy is not good

The disadvantage of these methods is that the glue is easy to block the micropores in the PE diaphragm, and it is easy to form an airtight skin layer. It is difficult to control the uniformity and consistency of the micropores during production; At 180-320°C, so it cannot be formed by polycondensation on the surface of the PE separator with a melting point of 135°C

[0007] Document CN 01116353.4, US 09 / 546266 and German Degussa Company proposed a technical method of composite porous layer of ceramic composite material and porous polymer layer that can be shut off. PET fibers are usually used to bond ceramic powder into a film by thermocompression. Considering that the thickness of the composite ceramic porous membrane is often more than 25 microns, it is easy to crack and lose powder during winding. Although ceramic powder can theoretically use the function of preventing internal dendrites from piercing the separator to prevent short circuit, the internal resistance of the battery is often too large. Poor electrochemical performance

[0008] In order to solve the above-mentioned technical problems, the inventor once proposed in the document CN 03100863.1 that a polyimide high-temperature-resistant porous film layer with micron-scale pores is produced separately, and then combined with a traditional polyolefin diaphragm with nano-scale pores. method, but due to the high brittleness and insufficient strength of the porous polyimide membrane, it is difficult to meet the requirements of the winding process

[0009] Documents CN 03125501.9, CN 02118877.7, JP 270620 / 2002, US 10 / 446380, CN200410035400.2, US 6322923, etc. proposed a method of forming a microporous membrane such as PVDF on the surface of a polyolefin microporous membrane to exert PVDF liquid absorption Good, good adhesion between the separator and the pole piece, and uniform ion conduction, which are good for fully utilizing the battery capacity and improving safety; however, if the PVDF porous film layer on the polyolefin microporous separator is too thin, the polyolefin When the microporous diaphragm is heat-shrinked, it is easy to shrink together with PVDF, which is not enough to prevent the short circuit of the internal pole pieces of the battery, and the safety is not high; if the PVDF porous film layer on the polyolefin microporous diaphragm is too thick, due to the combination of PVDF and polyolefin microporous The diaphragm has poor adhesion and is easy to peel off. This method is not conducive to mass production

[0010] Documents US 5603892 and CN 01112218.8 propose to inject the composition of polymer precursor and electrolyte into the lithium ion battery core, and perform thermochemical crosslinking by heating to form a thermochemical gel between the pole piece and the separator to improve The adhesion between the pole piece and the diaphragm can avoid uneven heating during overcharging. Thermochemical crosslinking has been successfully used in the manufacture of cable insulation jackets, but it is used in lithium-ion batteries due to the use of many monomers or polymer precursors. , crosslinking agent, peroxide initiator and other compositions, there are incomplete reactions, residues and impurities can easily affect the electrochemical performance of the battery, and it is difficult to control the quality of mass production

[0011] In order to solve the above-mentioned technical problems, the inventor proposed in the document CN 200410081129.6 a method for coating and manufacturing a PVDF porous film layer on the pole piece of a lithium-ion battery cell. This method avoids the above-mentioned shortcomings. The film has good adhesion and is not easy to peel off. In addition, the PVDF porous membrane layer has a low thermal shrinkage rate at 100-150 ° C, which can make up for the lack of high thermal shrinkage rate of high-strength polyolefin separators; There is a shortage of high production costs. In addition, due to the requirement to prevent thermal runaway inside the battery, it is hoped that the battery will have a high-temperature-resistant and low-heat-shrinkable separator that can prevent short-circuiting of the positive and negative electrodes at up to 200°C. This method is important for battery safety and economy. Sex still needs to be improved