Mass production of ultralight graphene films by electrophoretic deposition to improve performance of lithium-ion and lithium-sulfur batteries

Abstract

Graphene films are promising to improve cycle performance and rate capability of LiNi_0.5Mn_1.5O₄ (LNMO) and lithium‑sulfur (LiS) batteries. However, designing and fabricating ultralight and uniform graphene films directly on prepared electrodes or separators using simple, versatile, and high efficiency methods are still challenging. In this work, p-Phenylene diamine (pPD) reduced graphene oxide (pPD-rGO) films are deposited on the surface of LNMO electrode via electrophoretic deposition (EPD). The pPD-rGO modified LNMO electrode (LNMO/pPD-rGO), with the high LNMO loading (9 mg/cm²) and the ultralight pPD-rGO films loading (19 μg/cm²), remains 92.7 mAh/g with the capacity retention rate of 80.2 % after 1000th cycle at 1C. Moreover, a novel and unique EPD device is designed and assembled to present overlong and ultralight pPD-rGO and less defect graphene (LDG) films on commercial PP separators. The area density of pPD-rGO and LDG films are 17 and 100 μg/cm², only accounting for 0.9 % and 5.5 % of PP separator weight, respectively. The pPD-rGO modified PP separator (PP/pPD-rGO) using in LNMO electrode enhances the capacity retention rate of 1000th cycles from 66.2 % to 80.6 %. The LDG modified PP separator (PP/LDG) using in high sulfur loading electrode (5 mg/cm²) not only exhibits the capacity retention rate of 81.1 % after 150th at 0.2C, but also can deliver reversible capacity of 738.9 mAh/g with the decay rate per cycle of 0.068 % after 250th cycle at 0.5C. All results show these ultralight graphene films on electrode or separator by EPD can effectively improve the performance of batteries due to reducing interface impedance. This work not only demonstrates the feasibility of the strategy of graphene films surface modification, but also proclaims the potential of EPD application prospect in high specific energy batteries.