Graphene collage on Ni-rich layered oxide cathodes for advanced lithium-ion batteries

Abstract

The energy storage performance of lithium-ion batteries (LIBs) depends on the electrode capacity and electrode/cell design parameters, which have previously been addressed separately, leading to a failure in practical implementation. Here, we show how conformal graphene (Gr) coating on Ni-rich oxides enables the fabrication of highly packed cathodes containing a high content of active material (~99 wt%) without conventional conducting agents. With 99 wt% LiNi0.8Co0.15Al0.05O2 (NCA) and electrode density of ~4.3 g cm-3, the Gr-coated NCA cathode delivers a high areal capacity, ~5.4 mAh cm−2 (~38% increase) and high volumetric capacity, ~863 mAh cm-3 (~34% increase) at a current rate of 0.2 C (~1.1 mA cm-2); this surpasses the bare electrode approaching a commercial level of electrode setting (96 wt% NCA; ~3.3 g cm-3). Our findings offer a combinatorial avenue for materials engineering and electrode design toward advanced LIB cathodes.

Graphene/PVDF Composites for Ni-rich Oxide Cathodes toward High-Energy Density Li-ion Batteries

“…We prepared Gr dispersions by an electrochemical exfoliation method with commercially available graphite foils [ 15 , 16 , 17 ]. By applying a DC voltage (+10 V), a graphite foil was exfoliated into Gr sheets in an aqueous ammonium persulfate solution (0.5 M), due to the evolution of gases, such as SO 2 and O 2 .…”

“…The exfoliated Gr sheets have lateral sizes of 0.1–2 μm and an average thickness of 4.6 nm (refer to Figure S1 ). The Gr surface/edges appeared to be partially oxygen-functionalized (C–OH/C–O/C=O) due to the oxidation of graphite by OH – ions during the electrochemical process on the basis of XPS C 1s spectra ( Figure S2 ) [ 16 , 17 ]. We performed confocal Raman mapping on the exfoliated Gr sheets, which showed the high-intensity G peak and 2D peak at ~1580 and ~2700 cm −1 , respectively, with an intensity ratio of D to G (I D /I G ) of ~0.3 ( Figure S3 ), which is much lower than that of chemically or thermally reduced graphene oxides (I D /I G = 1.2–1.5) [ 15 , 18 , 19 ].…”

Graphene-Enhanced Battery Components in Rechargeable Lithium-Ion and Lithium Metal Batteries

“…Compared to pristine NMC811, the graphene composite exhibited higher capacity at 5 C (127 vs. 160 mA h g −1 , respectively) and a better cycle life. Park et al produced a conformal graphene coating on NCA and NMC811 particles by employing an amphiphilic surfactant, 1,2-distearoylsn-glycero-3-phosphoethanolamine-N-[methoxy(polyethyleneglycol) (DSPE-mPEG), which acts as a glue to bind the hydrophobic basal plane of graphene to the hydrophilic lithium hydroxide or lithium carbonate on the surface of NCA or NMC811 particles, as shown in Figure 11 [135]. Their results showed that the conformal graphene coating could eliminate the necessity of adding carbon blacks as conductive additives and thus a high active material content (99 wt.%) and, as a result, a high electrode density (~4.3 g cm −3 vs.~3.3 g cm −3 for 96 wt.% NCA electrode with the carbon black) were achieved.…”

“…The rate capability testing results of the two samples demonstrated opposite effects when compared to the pristine NCA: the sample coated with graphene nanodots showed improvement in capacity at all tested C-rates, while the rGO-coated sample displayed a lower capacity than that of the pristine sample at all tested C-rates. We summarize the results from two studies [135,136] that both used 0.5 wt.% graphene (or rGO) coating on NCA particles and present a visual comparison in Figure 12. The Y-axis represents the percentage of capacity changes defined as [(specific capacity of the coated sample)-(specific capacity of the non-coated sample)] divided by (specific capacity of the non-coated sample) at 0.1 C. The SEM micrographs clearly showed a more compact coating when the larger graphene (rGO) was used as the coating material.…”

Morphology and Chemical Purity of Water Suspension of Graphene Oxide FLAKES Aged for 14 Months in Ambient Conditions. A Preliminary Study

“…Graphene is a two-dimensional, one-atom-thick layer of carbon, in which atoms are oriented in a hexagonal crystal lattice. The promising and appealing properties of graphene-based materials are widely used in many research-oriented fields, like fuel cells [ 1 , 2 ], batteries [ 3 , 4 ], screens [ 5 , 6 ], sensors [ 7 , 8 ], flexible electronics [ 9 , 10 ], tissue engineering [ 11 , 12 ], and membranes [ 13 , 14 ]. Moreover, their unique features result in an increase of materials’ mechanical strength, electrical and thermal conductivity, and surface area and flexibility [ 15 , 16 , 17 ], making them the most preferred choice in experimental procedures.…”