Sepiolite-Assisted Separator Modification Process for High-Voltage LiNi0.5Mn1.5O4 Batteries and the Influence on Electrodes

The practical application of high-voltage LiNi0.5Mn1.5O4 is heavily restricted by serious capacity degradation, especially at high temperatures. Commercial polyolefin separators have shortcomings of poor electrolyte wettability and severe thermal shrinkage. In addition, polyolefin separators cannot prevent the penetration of lithium dendrites for lithium anodes, resulting in electrochemical performance degradation and potential safety concern for lithium-ion batteries. Herein, a homogeneous suspension containing sepiolite is electrospun onto the surface of a poly(propylene) (PP) substrate to produce a composite separator for high-voltage LiNi0.5Mn1.5O4 batteries. Different from previous research, the PP substrate is modified on single and double sides, respectively. The influence of a single-side coating separator on the cathode and the anode is studied. It is found that the sepiolite electrospinning layer can uniformly distribute the current density and form uniform lithium-ion deposition, which can avoid the growth of lithium dendrites. The different assembly directions of the single-side coating separator show great differences in battery performance. The LiNi0.5Mn1.5O4/Li battery using the single-side coating separator with the sepiolite electrospinning layer facing the Li anode shows better cycling stability (74.4% after 200 cycles at 55 °C), greatly alleviating the capacity fading of LiNi0.5Mn1.5O4 batteries at high temperature. The stable solid electrolyte interphase (SEI) layer on the anode surface plays a predominant role in the cycle life of the battery. The single-side coating separator with the sepiolite electrospinning layer facing the anode is more suitable for high-voltage LiNi0.5Mn1.5O4 batteries.