| Nowadays, the world-concerned problems are energy problem and environment problem. With a continuous consumption of traditional energy, the exploitation of renewable and clean energy is very important. Since the lithium ion secondary battery has the good features of high power density, high voltage, no memory effect, environment-friendly, low self-discharge and long cycle life, it is concerned to be a kind of clean energy which is being widely used now.Lithium-ion secondary battery is composed of cathode materials, anode materials, electrolyte and separators. This paper is focused on the separator of the lithium-ion secondary battery.The common methods for manufacturing the separatro are wet process and dry process. Separators made by the dry process have a distinct slit-pore and straight micro structure, and it is difficult to control the pore size and porosity, which is bad for the consistency of the lithium-ion secondary battery. The process of wet process is complex and solvent is needed to dissolve the polymer, which makes the environmental pollution.In this paper, we invented a new method for manufacturing the porous membranes. First, we prepared the silica needle arrays template by tube-array-etching (TAFE) method, and then pressing the template into the plastic wrap under the melting temperature of the polyolefin. A uniform porous membrane was prepared. The relationship between the hot-pressing pressure and the size of pore was invented, and we found that the size of the pore increased linearly as the pressure increased.Separators play an important role in lithium-ion secondary battery. Although the microporous polyolefin separators can meet most commercial usages in lithium-ion secondary battery, they have several drawbacks such as low thermal stability and poorly compatibility with liquid electrolytes, which restrict the further use of the lithium ion secondary battery, especially in the field of electric vehicles development.In this paper, atomic layer deposition (ALD) method and dip coating method are used to obtain Al2O3 inorganic coatings and PVDF-HFP organic coatings respectively. The coating layers give rise to the improvement of the liquid-affinity and thermal stability of the separators significantly.Alumina inorganic composite separator was used by ALD. We prepared the composite separator with one-side alumina coating and double-side alumina coating with the thickness of the coating layer from 5nm to 20nm. We found that the double-side coating composite separators performed better everywhere than that of the one-side coating. The composite separator enhanced the thermal property, mechanical stability, electrolyte uptake, electrolyte retention, electrical performance. We found that a 5 nm or 10 nm alumina coating made best for the separator. Electrolyte uptake and retention were increased many times than the original separator. The composite separator decreased the thermal shrinkage significantly with no shrinkage under 160℃, which could improve the safety of the batteries. The capacity of the cells made by the 5 nm alumina coating and the 10 nm alumina coating composite separators were 136.68 mAh/g and 137.71 mAh/g at 0.1C,114.48 mAh/g and 119.77 mAh/g at 1C,95.90 mAh/g and 107.56 mAh/g at 2C. What’s more, the capacity retention of the cells made by the 5 nm alumina coating and the 10 nm alumina coating composite separators were 96.05% and 96.92% after 50 cycles at 1C.PVDF-HFP composite separators were prepared by phase inversion method. We investigated the effects of the polymer’s mass fraction, the composition of the casting solution and the composition of the coagulating bath on the pores structure. We selected several composite separators with excellent structures for further test. Electrolyte uptake and retention, thermal stability property and cell performances were measured, and the composite separators performed better than the original separator. |
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