(407f) Cross-Linked Reduced Graphene Oxide Aerogels and Their Applications As 3D Electrodes for Lithium-Ion Batteries

Lithium-ion batteries (LIBs) are ubiquitous as they are the cornerstone of many electronic devices, such as smartphones, smartwatches, laptops, and power tools, due to their relatively low cost, good energy density, and slow self-discharge rates. While the battery cycling performance of conventional LIBs is satisfactory for some applications, challenges still exist to manufacture safe, light-weight, and more durable batteries to be used in places where a high performance-weight ratio is important, such as in aerospace and electric vehicles.

The energy density (energy per unit mass) of conventional LIBs is often limited by so-called electrochemically inactive materials, such as the binder, separator, current collectors, and battery casing. While increasing the mass loading/thickness of the active material (such as LiCoO₂ in the cathode of an iPhone battery) is a direct way to mitigate this loss in energy density, the Li-ion diffusion rate and the mechanical integrity of thick electrodes are often limiting. As such, the electrode thickness in conventional LIBs is restricted to ~100—125 μm. While developing novel active materials with greater theoretical capacity is important for improving the energy density of LIBs, such materials are often very expensive and can only be produced in labs, which is not favorable from a commercialization point of view.

Our work focuses on improving the energy density by substituting the metal current collectors with a three-dimensional, light-weight, mechanically robust, porous and conductive poly(acrylic acid)/reduced graphene oxide aerogel (further referred as rGO-XPAA aerogel). This aerogel has a bulk density of 6 mg/cm³ and a porosity of 99.6%, and the thermally cross-linked poly(acrylic acid) (PAA) on the aerogel structure makes it elastic and mechanically robust.

Commercially available active materials, LiNi_1/3Co_1/3Mn_1/3O₂ (NCM) and Li₄Ti₅O₁₂ (LTO), were used to fabricate metal-free current collectors/electrodes with tunable mass loading (~ 3-30 mg/cm²) and thickness (~ 30-130 µm). The electrodes can withstand ~ 100-fold compression (from ~3 mm to 30 µm) and achieve a high volumetric energy density of 1723 Wh/L for NCM and 625 Wh/L for LTO, which represents ~25% increase in energy density over their conventional counterparts.