CN-121584149-B - Preparation method of high-thermal-safety lithium battery diaphragm based on magnesium-based whisker

Abstract

The invention discloses a preparation method of a high-heat-safety lithium battery diaphragm based on magnesium-based whiskers, and belongs to the field of lithium battery diaphragms. According to the invention, the magnesium-based whisker, particularly the self-made basic magnesium sulfate whisker is introduced to obtain oily mixed slurry, the oily mixed slurry is coated on two sides of a polyolefin porous substrate to form an oily coating, and the lithium battery diaphragm is obtained after drying. The invention has simple process, and the prepared composite diaphragm has excellent electrolyte wettability, high ion conductivity, high lithium ion migration number, excellent thermal shrinkage resistance and flame retardance.

Inventors

• ZHU JIXIN
• OU MINGYU
• WANG YISHA

Assignees

• 中国科学技术大学

Dates

Publication Date

20260505

Application Date

20260127

Claims (4)

1. 1. A preparation method of a high-heat-safety lithium battery diaphragm based on magnesium-based whiskers is characterized by comprising the following steps: Adding magnesium-based whiskers into the slurry of the binder polymer and uniformly mixing to obtain oily mixed slurry, coating the oily mixed slurry on two sides of a polyolefin porous substrate to form an oily coating, and drying to obtain a lithium battery diaphragm; the magnesium-based whisker is basic magnesium sulfate whisker and is prepared by a method comprising the following steps: Step 1, dissolving magnesium sulfate heptahydrate and magnesium chloride hexahydrate in deionized water to prepare a mixed salt solution, adding disodium ethylenediamine tetraacetate into the mixed salt solution, and stirring until the mixture is uniform to obtain a solution A; Step 2, weighing NaOH, dissolving in deionized water to prepare a solution B, dropwise adding the solution B into the solution A under vigorous stirring, continuously stirring to form uniform precursor slurry, transferring the precursor slurry into a polytetrafluoroethylene-lined hydrothermal reaction kettle for hydrothermal reaction, naturally cooling the reaction kettle to room temperature after the reaction is finished, repeatedly washing the product by suction filtration and deionized water until no SO 4 2- and Cl - remain, and vacuum drying a filter cake to obtain a basic magnesium sulfate whisker product with high length-diameter ratio; In the step 1, the mol ratio of the magnesium sulfate heptahydrate to the magnesium chloride hexahydrate is 7:3, and the concentration of magnesium ions in the mixed salt solution is 0.8-1 mol/L; In the step 1, when disodium ethylenediamine tetraacetate is added, controlling the molar ratio of Mg 2+ to disodium ethylenediamine tetraacetate to be 20:1; In the step 2, when the solution B is dripped into the solution A, controlling the mol ratio of Mg 2+ to OH - to be 1:1.2; the length L of the magnesium-based whisker is 50-90 mu m, the diameter d is 0.6-1 mu m, and the length-diameter ratio L/d is 50-90.
2. 2. The method of manufacturing according to claim 1, characterized in that: in the step 2, the reaction temperature of the hydrothermal reaction is 160 ℃ and the reaction time is 10 hours.
3. 3. The method of manufacturing according to claim 1, characterized in that: the binder polymer is one or more of styrene-butadiene rubber, acrylic resin, polyvinyl alcohol, polyacrylonitrile, polyvinylidene fluoride, carboxymethyl cellulose, polyethylene oxide and polytetrafluoroethylene.
4. 4. The method of manufacturing according to claim 1, characterized in that: The mass volume ratio of the magnesium-based whisker, the binder polymer and the solvent is (150-250) mg (20-40) mg (1-1.5) mL.

Description

Preparation method of high-thermal-safety lithium battery diaphragm based on magnesium-based whisker Technical Field The invention belongs to the technical field of lithium battery diaphragms, and particularly relates to a preparation method of a high-heat safety lithium battery diaphragm based on magnesium-based whiskers. Background The rapid development of electric vehicles and energy storage systems has driven the need for higher energy density and safer batteries. Conventional lithium ion batteries, although widely used, are limited by the limitations of the capacity of graphite cathodes. In contrast, metallic lithium has an ultra-high theoretical capacity (3830 mAh g -1) and an extremely low reduction potential (-3.04V vs RHE), making it an ideal negative electrode material for a new generation of batteries. However, the formation of unstable solid electrolyte interface layers (SEI) and the growth of irreversible lithium dendrites during cycling severely limit the commercial application of lithium metal batteries. These problems not only shorten the battery life, but are more likely to mechanically puncture the separator to cause internal short circuits, resulting in locally rapid temperature increases. When the temperature rises sharply, the organic electrolyte can decompose to produce flammable gases (e.g., H 2 and CH 4) and a large number of reactive radicals (e.g., HO. And H. Cndot.). These combustible substances then undergo a severe exothermic reaction with oxygen released from the thermally unstable cathode material at about 200 ℃ and eventually cause thermal runaway. In addition, highly flammable polymeric membranes can also generate additional flammable toxic gases (such as hydrocarbons and CO), further exacerbating fire and explosion risks. These coupling failure modes, including uncontrolled dendrite growth, unstable SEI film formation and serious safety hazards, together constitute a major obstacle to practical safety applications of lithium metal batteries, highlighting the need to formulate effective strategies to develop rechargeable batteries with both high energy density and safety. To solve dendrite formation and instability problems of lithium metal anodes, various solutions have been developed, such as additive optimization of the electrolyte, formation of artificial SEI/coating on the surface of the lithium metal, construction of three-dimensional porous frames, and use of solid electrolytes. However, these methods either face technical barriers or introduce new challenges such as high cost, complex process, limited scalability, etc. Compared with other strategies, the functional membrane engineering is intrinsically simpler and highly scalable. However, the conventional polyolefin separator (polyethylene or polypropylene) has problems of poor electrolyte wettability and low ion conductivity, which aggravates concentration polarization and causes lithium deposition unevenness during electrochemical cycling. In addition, the conventional polyolefin separator has inherent disadvantages of high flammability and poor heat shrinkage resistance. Polyolefin membranes are susceptible to thermal shrinkage and commercial CELGARD PP membranes have a melting point of about 160-165 ℃ beyond which structural integrity is lost. In order to solve the above problems, there have been studies on compounding inorganic whiskers in a separator slurry/coating system in the prior art, but the inorganic whiskers used are generally low in aspect ratio and unevenly distributed. Limited to the preparation process of industrialized large-scale precipitation, commercial whiskers often exhibit short rods or irregular platelets, with aspect ratios typically less than 30. Such low aspect ratio particles have difficulty building an effective "three-dimensional interpenetrating network backbone" on the polyolefin-based film surface during coating. Instead, they tend to form dense stacks or undergo severe agglomeration at the membrane surface, thereby physically blocking the micropores of the base membrane. This directly results in a decrease in porosity of the composite separator, and insufficient electrolyte absorption and retention, thereby significantly increasing ion transport resistance and limiting the increase in ion conductivity and lithium ion migration number. Second, the surface state of commercial whiskers is detrimental to the development of electrochemical performance. To prevent agglomeration and facilitate storage, commercial whisker surfaces often have impurities adsorbed or been hydrophobicized, lacking active polar sites. This makes it less compatible with the electrolyte and does not effectively regulate the solvated sheath structure of lithium ions. The battery assembled by the commercial whisker modified diaphragm has serious polarization and rapid capacity decay (for example, the capacity retention rate is difficult to maintain above 80%) in the long cycle process, and the lithium dendrite gro