Katz Michelle E R, Cobb Corie L
Department of Mechanical Engineering, University of Washington, Seattle, Washington 98195, United States.
ACS Appl Mater Interfaces. 2024 Aug 28;16(34):44863-44878. doi: 10.1021/acsami.4c09342. Epub 2024 Aug 13.
Separators play a critical role in lithium-ion batteries (LIBs) by facilitating lithium-ion (Li-ion) transport while enabling safe battery operation. However, commercial separators made from polypropylene (PP) or polyethylene (PE) impose a discrete processing step in current LIB manufacturing as they cannot be manufactured with the same slot-die coating process used to fabricate the electrodes. Moreover, commercial separators cannot accommodate newer manufacturing processes used to produce leading-edge microbatteries and flexible batteries with customized form factors. As a path toward rethinking LIB fabrication, we have developed a high-viscosity polymer composite separator slurry that enables the fabrication of both freestanding and direct-on-electrode films. A streamlined phase inversion process is used to impart porosity in cast separator films upon drying. To understand the impacts of material composition and rheology on phase inversion processing and separator performance, we investigated four different separator formulations. We used either diethylene glycol (DEG) or triethyl phosphate (TEP) as a nonsolvent, and either silica (SiO) or alumina (AlO) as an inorganic additive in a polyvinylidene fluoride--hexafluoropropylene (PVDF-HFP) matrix. Through a down-selection process, we developed a TEP-SiO separator formulation that matched or outperformed a commercial Celgard 2325 (PP/PE/PP) separator and a Beyond Battery ceramic-coated PE (CC/PE/CC) separator under rate and cycle life tests in LiFePO|LiTiO (LFP|LTO) and LiNiMnCoO|graphite (NMC-532|graphite) coin cells at C/10-1C rates. Our TEP-SiO slurry had a viscosity of 298 Pa s at a 1 s shear rate and shear-thinning behavior. When deposited directly onto an LTO anode and cycled against an LFP cathode, the direct-on-electrode TEP-SiO separator increased the specific capacity by 58% and 304% at 2C rates relative to the PP/PE/PP and CC/PE/CC separators, respectively. Additionally, the freestanding TEP-SiO separator maintained dimensional stability when heated to 200 °C for 1 h and demonstrated a higher elastic modulus and hardness than the PP/PE/PP and CC/PE/CC separators when measured with nanoindentation.
隔膜在锂离子电池（LIBs）中起着关键作用，它有助于锂离子传输，同时确保电池安全运行。然而，由聚丙烯（PP）或聚乙烯（PE）制成的商用隔膜在当前LIB制造过程中需要一个单独的加工步骤，因为它们无法采用与制造电极相同的狭缝模头涂布工艺进行制造。此外，商用隔膜无法适应生产具有定制外形的前沿微电池和柔性电池所采用的更新制造工艺。作为重新思考LIB制造的一条途径，我们开发了一种高粘度聚合物复合隔膜浆料，可用于制造独立式和直接涂覆在电极上的薄膜。采用一种简化的相转化工艺，在干燥时赋予浇铸隔膜薄膜孔隙率。为了解材料组成和流变学对相转化过程和隔膜性能的影响，我们研究了四种不同的隔膜配方。在聚偏氟乙烯-六氟丙烯（PVDF-HFP）基体中，我们使用二甘醇（DEG）或磷酸三乙酯（TEP）作为非溶剂，并使用二氧化硅（SiO）或氧化铝（AlO）作为无机添加剂。通过筛选过程，我们开发了一种TEP-SiO隔膜配方，在LiFePO|LiTiO（LFP|LTO）和LiNiMnCoO|石墨（NMC-532|石墨）扣式电池中，在C/10-1C倍率下的倍率和循环寿命测试中，该配方与商用Celgard 2325（PP/PE/PP）隔膜和Beyond Battery陶瓷涂覆PE（CC/PE/CC）隔膜相当或更优。我们的TEP-SiO浆料在1 s剪切速率下的粘度为298 Pa·s，具有剪切变稀行为。当直接沉积在LTO阳极上并与LFP阴极进行循环时，直接涂覆在电极上的TEP-SiO隔膜在2C倍率下的比容量相对于PP/PE/PP和CC/PE/CC隔膜分别提高了58%和304%。此外，独立式TEP-SiO隔膜在加热至200°C并保持1 h时保持尺寸稳定性，并且在用纳米压痕测量时，其弹性模量和硬度高于PP/PE/PP和CC/PE/CC隔膜。
