Reduced graphene oxide networks as an effective buffer matrix to improve the electrode performance of porous NiCo2O4 nanoplates for lithium-ion batteries

Abstract

Transition metal oxides are promising high-capacity anode materials for next-generation lithium-ion batteries. However, their cycle life remains a limiting factor with respect to their commercial applications. The development of transition-metal oxide anode materials with long lifespans through a facile route has become an important issue. A straightforward strategy is designed for the fabrication of a NiCo 2 O 4 nanoplates-reduced graphene oxide sheets (NiCo 2 O 4 -RGO) composite. It displays a high reversible capacity of 816 mA h g À1 over 70 cycles with 80.1% capacity retention of the 2nd cycle and excellent rate capability. Its rate capability and cycling stability are enhanced in comparison with those of pure NiCo 2 O 4 nanoplates. The as-obtained nanocomposite avoids the problems of dispersion and aggregation induced by cracking or pulverization of the transition-metal oxide upon cycling. The graphene or reduced graphene oxide not only works as a substrate to provide room for loading scattered grains, but also serves as a conductive network to facilitate the collection and transportation of electrons during the cycling, indirectly increasing the conductivity of NiCo 2 O 4 .

How to improve the stability and rate performance of lithium-ion batteries with transition metal oxide anodes

“…The initial charge and discharge capacities are approximately 1187 and 1859 mA h/g, respectively, resulting in an initial coulombic efficiency of ;64%. The initial irreversible capacity loss of the Co 3 O 4 @C@PGC nanosheets could be associated with the inevitable formation of SEI and decomposition of electrolyte 8,9,85,89 and in good agreement with the above CV results. The discharge voltage plateau at ;1.1 V in the first cycle shift to ;1.2 V since the second cycle, just corresponding to the shift of reduce peak in CV curves from 0.97 V to 1.15 V. The areas under the charge and discharge curves are comparable, indicating a very low energy loss during charge/discharge.…”

“…The large volumetric change of NiCoO 2 during lithiation/delithiation can be accommodated by the flexible rGO and the room between the sandwich sheets. 8,56 As the NiCoO 2 sheets are firmly anchored with rGO, even if the NiCoO 2 sheets pulverized during cycling, they wouldn't peel off from the surface of rGO. Thus, the electrode materials are still active, and the integration of the electrode remains stable.…”

“…However, the NPs are still prone to aggregate during cycling because of nonintimate/tight contact between the NPs and graphene sheets (GS) layers. 8,38 On the other hand, the overlapping of GS during electrode preparation and electrochemical test is also a critical problem, which may result in inadequate adhibition of graphene. Therefore, to adequately utilize the unique properties of individual GS and fully harness the synergistic effect between GS and M x O y , the main challenges in the synthesis of graphene/M x O y composites lie in how to effectively enhance the contact between GS and M x O y and inhibit too much overlapping and agglomeration of GS.…”

“…[8][9][10][11][12][13][14][15][16][17] are considered as feasible anode alternatives due to the high-specific capacities induced by conversion reaction mechanism, which was first proposed and elucidated by Poizot et al 18 However, they have relatively poor electrical conductivity and their volume change a lot during the Li 1 insertion and extraction. 19 Poor conductivity always leads to bad rate performance and low power density.…”

Surfactant-assisted solvothermal synthesis of NiCo2O4 as an anode for lithium-ion batteries

“…However, the reported reversible capacity for NiCo 2 O 4 hollow spheres and nanosheets and so on is not up to 600 mA h g À1 at large current density of 1000 mA g À1 . 21,23,24 Different from the above synthetic methods, microemulsion approach equips with large interfacial area and ultralow interfacial tension. Solvothermal synthesis of nanomaterials can not only reduce the reaction temperatures, but also improve the crystallinity of the products.…”