【Ten Years of Great Progress in Chemical Technology】165-2023: Special material for lithium-ion battery separators made from ultra-high molecular weight polyethylene (UHMWPE)

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The lithium battery separator determines key parameters such as the battery’s service life, cycle performance, and safety, making it one of the most crucial internal components in the lithium battery industry chain. Diaphragm products made from ultra-high molecular weight polyethylene (UHMWPE) exhibit excellent electrochemical stability, long service life, high safety, thin and uniform thickness, as well as easy control over pore size; they have gradually become the mainstream in the development of lithium battery diaphragms. To ensure the safety performance of lithium battery separators, while also taking into account the uniformity of material plasticization, film-forming properties, and thermal stability, the polyethylene used in specialized materials for lithium battery separators is required to have an average molecular weight ranging from 500,000 to 800,000, with this value gradually increasing to over 1,000,000. However, due to limitations in production technology, domestic wet-process diaphragm manufacturers rely mainly on imported UHMWPE resin for their production. Domestic materials fall far short of imported ones in terms of performance and influence, owing to difficulties in controlling the ultra-high molecular weight process, stringent requirements for the core properties of the products, and long approval times required by end-users. In May 2023, UH100P and UH150P – specialized materials for lithium-ion battery separators made from ultra-high molecular weight polyethylene (UHMWPE) – which were developed through a collaboration between the China National Petroleum Corporation’s Research Institute of Petrochemicals (hereinafter referred to as the Research Institute) and Daqing Petrochemical Company – were produced for the first time in a low-pressure polyethylene plant with an annual capacity of 220,000 tons. The various performance parameters of the product meet the specified requirements, with the average molecular weight being 1 million and 1.5 million respectively, indicating that the Petrochemical Research Institute has successfully embarked on the path of independent research and development for a full range of new UHMWPE products. 　　To this end, the Resin Research Institute of the Daqing Center at the Petrochemical Research Institute adopted a development strategy that combines the use of self-developed small-particle catalysts with the industrial application of existing catalysts, thereby achieving innovative progress in the development and production of materials specifically designed for UHMWPE lithium battery separators and accelerating the process of industrial production. In 2022, the Petrochemical Research Institute conducted in-depth research on market supply and demand trends as well as customer feedback. During the development process, it focused on addressing technical challenges such as the particle size and uniform distribution of specialty material particles, further optimizing relevant technical parameters, and developing the production technologies for UH100P and UH150P. 　　Since early April, the project team members, together with the technical staff from Daqing Petrochemical Company, have developed a detailed industrial application test plan based on the characteristics of the catalyst and the desired grade. During production, they remained on site, closely monitoring the product parameters, and continuously conducting tests on properties such as particle size distribution, melting point, melt index, and density – providing important data for timely adjustments to the process parameters. At present, the specialized material for UH100P has been successfully tested in small-scale tonnage-level processing by domestic lithium battery diaphragm manufacturers, and efforts are being accelerated to advance the pilot-scale processing tests for 10-tonne capacity diaphragms; discussions regarding processing cooperation with downstream manufacturers are also underway for the UH150P product. 　　The successful development of specialized materials for the UH100P and UH150P models has paved the way for the research and development of a new range of UHMWPE products, opening up new avenues for the creation of high-end polyolefin products. It also makes a significant contribution to helping petrochemical companies improve their quality and efficiency. Next, the Petrochemical Research Institute will continue to innovate in the development of new high-end polyolefin products, optimize the product portfolio, and enhance its market competitiveness.