Camphene-Assisted Fabrication of Free-Standing Lithium-Ion Battery Electrode Composites.

Free-standing electrode (FSE) architectures hold the potential to dramatically increase the gravimetric and volumetric energy density of lithium-ion batteries (LIBs) by eliminating the parasitic dead weight and volume associated with traditional metal foil current collectors. However, current FSE fabrication methods suffer from insufficient mechanical stability, electrochemical performance, or industrial adoptability. Here, we demonstrate a scalable camphene-assisted fabrication method that allows simultaneous casting and templating of FSEs comprising common LIB materials with a performance superior to their foil-cast counterparts. These porous, lightweight, and robust electrodes simultaneously enable enhanced rate performance by improving the mass and ion transport within the percolating conductive carbon pore network and eliminating current collectors for efficient and stable Li+ storage (>1000 cycles in half-cells) at increased gravimetric and areal energy densities. Compared to conventional foil-cast counterparts, the camphene-derived electrodes exhibit ∼1.5× enhanced gravimetric energy density, increased rate capability, and improved capacity retention in coin-cell configurations. A full cell containing both a free-standing anode and cathode was cycled for over 250 cycles with greater than 80% capacity retention at an areal capacity of 0.73 mA h/cm2. This active-material-agnostic electrode fabrication method holds potential to tailor the morphology of flexible, current-collector-free electrodes, thus enabling LIBs to be optimized for high power or high energy density Li+ storage. Furthermore, this platform provides an electrode fabrication method that is applicable to other electrochemical technologies and advanced manufacturing methods.

Electrode Degradation in Lithium-Ion Batteries.

Although Li-ion batteries have emerged as the battery of choice for electric vehicles and large-scale smart grids, significant research efforts are devoted to identifying materials that offer higher energy density, longer cycle life, lower cost, and/or improved safety compared to those of conventional Li-ion batteries based on intercalation electrodes. By moving beyond intercalation chemistry, gravimetric capacities that are 2-5 times higher than that of conventional intercalation materials (e.g., LiCoO2 and graphite) can be achieved. The transition to higher-capacity electrode materials in commercial applications is complicated by several factors. This Review highlights the developments of electrode materials and characterization tools for rechargeable lithium-ion batteries, with a focus on the structural and electrochemical degradation mechanisms that plague these systems.

Carbon Nitride Transforms into a High Lithium Storage Capacity Nitrogen-Rich Carbon.

We describe here the metal-templated transformation of carbon nitride (C3N4) into nitrogen-containing carbons as anodes for Li-ion batteries (LIBs). Changing the template from the carbon- and nitrogen-immiscible Cu powder to the carbon- and nitrogen-miscible Fe powder yields different carbons; while Fe templating produces graphitized carbons of low (<10%) nitrogen content and moderate pore volume, Cu templating yields high defect-density carbons of high (32-24%) nitrogen content and larger pore volume. The Li+ storage capacity of the high nitrogen content and larger pore volume Cu-templated carbons exceeds that of the more graphitic Fe-templated carbons due to added contribution from Li+ insertion/extraction from pores and defects and to reversible faradaic Li+ reaction with nitrogen atoms. The Cu-templated carbon annealed at 750 °C delivers the highest specific capacity of 900 mAh g-1 at 0.1 A g-1 and 275 mAh g-1 at 20 A g-1, while also achieving a 96% capacity retention after 2000 cycles at 2 A g-1. The fabrication of higher mass loading electrodes (4.5 mg cm-2) provided a maximum areal capacity of 2.6 mAh cm-2 at 0.45 mA cm-2 (0.1 A g-1), comparable to the capacities of commercial LIB cells and favorable compared to other reported carbon materials.

Reduced-Graphene Oxide/Poly(acrylic acid) Aerogels as a Three-Dimensional Replacement for Metal-Foil Current Collectors in Lithium-Ion Batteries.

We report the synthesis and properties of a low-density (∼5 mg/cm3) and highly porous (99.6% void space) three-dimensional reduced graphene oxide (rGO)/poly(acrylic acid) (PAA) nanocomposite aerogel as the scaffold for cathode materials in lithium-ion batteries (LIBs). The rGO-PAA is both simple and starts from readily available graphite and PAA, thereby providing a scalable fabrication procedure. The scaffold can support as much as a 75 mg/cm2 loading of LiFePO4 (LFP) in a ∼430 µm thick layer, and the porosity of the aerogel is tunable by compression; the flexible aerogel can be compressed 30-fold (i.e., to as little as 3.3% of its initial volume) while retaining its mechanical integrity. Replacement of the Al foil by the rGO-PAA current collector of the slurry-cast LFP (1.45 ± 0.2 g/cm3 tap density) provides for exemplary mass loadings of 9 mgLFP/cm2 at 70 µm thickness and 1.4 g/cm3 density or 16 mgLFP/cm2 at 100 µm thickness and ∼1.6 g/cm3 density. When compared to Al foil, the distribution of LFP throughout the three-dimensional rGO-PAA framework doubles the effective LFP solution-contacted area at 9 mg/cm2 loading and increases it 2.5-fold at 16 mg/cm2 loading. Overall, the rGO-PAA current collector increases the volumetric capacity by increasing the effective electrode area without compromising the electrode density, which was compromised in past research where the effective electrode area has been increased by reducing the particle size.