热辊压对锂离子电池正极极片性能的影响

Influence of heated calendering process on cathode film performance of lithium-ion batteries

利用磷酸铁锂动力锂离子电池生产产线设备进行正极片制备,辊压工序分别将主辊温度设置为25℃、60℃、80℃、100℃、120℃,在相同主辊压力下将涂布后极片辊压至同一厚度,而后将相应极片制备成扣式电池并综合对比极片的各性能指标。结果表明热辊压对极片延展率无影响,但是会在一定程度上对辊压厚度均一性有所改善;热辊压能够降低极片的电阻,相比于常温辊压极片,100℃时极片电阻约下降2.1%;同时,热辊压可减小极片辊压后的厚度反弹,以60℃和100℃时最优,反弹率约为25℃时的一半;剥离力随辊压温度呈现先上升后下降的趋势,在60℃附近达到最高点。从扣电的性能上看,热辊压可有效降低电芯的欧姆阻抗和电荷传递阻抗,在100℃左右时最佳,这与极片膜片电阻结果一致;同时热辊压后的极片在倍率性能上也表现得更加出色,以100℃左右时最佳,但从100周循环数据上看,热辊压后极片所制扣电与常温辊压极片所制扣电无明显差别。综合各主辊温度下辊压所制极片和扣电在各性能测试中的表现,热辊压对极片和电芯性能有正向的改进作用,效果在100℃左右时达到最优。

The cathode film for lithium-ion batteries is fabricated using lithium iron phosphate powder on a production line.During the calendering process,the roll temperature is set to 25℃,60℃,80℃,100℃,and 120℃,respectively,and the cathode film is rolled to a uniform thickness under consistent roll pressure.Subsequently,the cathode film is fashioned intoCR2032 button batteries for evaluation.Parameters such as thickness uniformity,film resistance,peeling force,thickness rebound,elongation,and scanning electron microscopy(SEM)analyses are assessed.Additionally,electrochemical impedance spectroscopy(EIS),0.1—2C rate performance,and short-term 1C cycle performance are characterized to ascertain the impact of heated calendering on cathode film and cell performance,and to identify the optimal calendering temperature.Findings indicate that heated calendering does not affect the elongation of the cathode film;however,it enhances the uniformity of film thickness.The process also diminishes the resistance of the cathode film,with the optimal reduction observed at 100℃,approximately 2.1%.Moreover,heated calendering reduces thickness rebound,with the lowest rates at 60℃ and 100℃,approximately half of that at 25℃.The peeling force initially increases and then decreases with roll temperature,peaking near 60℃.SEM images reveal tighter binding of active materials postheated calendering compared to normal temperature processes,without grain breakage.Heated calendering effectively lowers both ohmic and charge-transfer impedance,with optimal results at around 100℃,correlating with film resistance observations.Enhanced rate performance is also noted in cathode films subjected to heated calendering,particularly at 100℃.However,no significant differences are observed in the cycle performance data over 100 cycles between cathode films produced via heated and normal calendering.Overall,heated calendering positively influences both film and cell performance,with the most beneficial effects at approximately 100℃.