The carbon net negative conversion of biochar, the byproduct of pyrolysis bio-oil production from biomass, to very high-purity (99.95%), highly crystalline flake graphite that is essentially indistinguishable from high-grade commercial Li-ion grade graphite, is reported. The flake size of the graphite is determined by the physical dimensions of the metal particles imbedded in the biochar, demonstrated in the range of micrometers to millimeters. “Potato”-shaped agglomerates of graphite flakes result when the flake diameter is in the 1–5 μm range. The process is shown to work with a variety of biomass, including raw lignocellulose (sawdust, wood flour, and corn cob) and biomass components (cellulose and lignin), as well as lignite. The synthesis is extremely rapid and energy efficient (0.25 kg/kWh); the graphite is produced with a very high yield (95.7%), and the energy content of its coproduct, bio-oil, exceeds that needed to power the process. The demonstrated process is a tremendous advance in the sustainability of graphite production, currently commercially mined or synthesized with very high environmental impacts, and results in a value-added product that could economically advantage carbon-neutral bio-oil production.

The carbon net negative conversion of bio-char, the low value byproduct of pyrolysis bio-oil production from biomass, to high value, very high purity, highly crystalline flake graphite agglomerates with rationally designed shape and size tailored for lithium-ion battery energy storage material is reported. The process is highly efficient, 0.41 g/Wh; the energy content of its co-product of the process, bio-oil, exceeds that needed to power the process. It is shown that the shape of the starting material is retained during the transformation, allowing the ultimate morphology of the graphite agglomerates to be engineered from relatively malleable biomass. In contrast to commercial graphite production, the process can be performed at small scale with low equipment costs, enabling individual research laboratories to produce Li-ion grade graphite with customizable shape, size and porosity for Si/graphite composite and other graphite involved anodes. The mechanism of the graphitization of bio-char, a “non-graphitizable” carbon, is explored, suggesting the molten metal catalyst is absorbed into the pore structure, transported through and transforming the largely immobile biochar. Finally, the transformation of biomass to rationally designed graphite morphologies with Li-ion anode performance that closely mimic commercial shaped graphite is demonstrated.

Understanding the transformation of graphitic carbon nitride (g-C3N4) is essential to assess nanomaterial robustness and environmental risks. Using an integrated experimental and simulation approach, our work has demonstrated that the photoinduced hole (h+) on g-C3N4 nanosheets significantly enhances nanomaterial decomposition under •OH attack. Two g-C3N4 nanosheet samples D and M2 were synthesized, among which M2 had more pores, defects, and edges, and they were subjected to treatments with •OH alone and both •OH and h+. Both D and M2 were oxidized and released nitrate and soluble organic fragments, and M2 was more susceptible to oxidation. Particularly, h+ increased the nitrate release rate by 3.37–6.33 times even though the steady-state concentration of •OH was similar. Molecular simulations highlighted that •OH only attacked a limited number of edge-site heptazines on g-C3N4 nanosheets and resulted in peripheral etching and slow degradation, whereas h+ decreased the activation energy barrier of C–N bond breaking between heptazines, shifted the degradation pathway to bulk fragmentation, and thus led to much faster degradation. This discovery not only sheds light on the unique environmental transformation of emerging photoreactive nanomaterials but also provides guidelines for designing robust nanomaterials for engineering applications.

The pyrolysis of cellulose produces bio-fuels, a net carbon neutral energy source, and bio-char that can be used as a soil enhancer. The economic feasibility of the production of bio-fuel from fast growing plants that can grow rapidly on minimally viable land, such as switch grass, would be greatly enhanced by producing higher added value products from the bio-char. Pyrolyzing bio-char in the presence of metal halide catalysts with a CO2laser for a few seconds results in the production of hollow graphene nanoshells (HGNS), a carbon negative material, which can be used in place of graphite active materials in Li-ion battery anodes with remarkably higher charge rate capability and low temperature performance in relatively inexpensive electrolytes. Graphite is the most widely used anode active material in commercial Li-ion batteries. With a standard reduction potential of -2.9 V vs SHE and theoretical gravimetric capacity of 372 mAh/g (at LiC6) it provides 2 to 3 times the energy density compared to aqueous battery chemistries. The challenge remains to charge graphite anodes at the very high rates required for applications such as electric vehicles while maintaining its capacity over thousands of cycles. Shortening the Li-ion diffusion distance in graphite crystallites allows one to increase the charging rate, however, small graphite particles have poor cycle life. We utilize hollow graphene nanoshells that have orders of magnitude shorter diffusion distances than standard graphite as an anode active material. These HGNS are made up of concentric multilayer graphene shells ~50 nm in diameter that intercalate Li+ in manner analogous to graphite but with remarkably higher charge rate capability (up to 22% charge in 7.2 s) and low temperature performance in relatively inexpensive electrolytes such as PC. Unfortunately, the storage capacity for HGNS is lower than graphite (~220 mAh/g vs. ~330 mAh/g practical), which motivated us to investigate synthetic variation to improve HGNS. Here we will present the results of our studies, finding that simple, inexpensive modifications to the synthetic procedures can result in HGNS with 40% greater reversible capacity (320 mAh/g) with no capacity loss after 100 cycles and a Coulombic efficiency of 99.9%. This new form of carbon is a very promising anode active material that could enable Li-ion batteries with dramatically faster charging rates, longer cycle lives and much better low temperature performance than standard graphite anodes. Furthermore, adoption of this carbon negative material in place of synthetic graphite could have a significant impact on global climate change, both directly by CO2 sequestration and indirectly by improving the economic viability of bio-fuels. Figure 1

The Li-ion battery provides the majority of powertrain energy for today’s electric vehicles (EVs). The usable range of EVs is largely limited by the Li-ion storage capacity in a Li-ion cell. In addition to low range, most EVs require 4 - 12 hours of charge time. Silicon, a Li-alloy alternative anode, has much greater gravimetric and volumetric capacities compared to graphite (3579 mAh/g vs. 372 mAh/g and 8335 mAh/cm3 vs. 818 mAh/cm3 for Li15Si4 vs. LiC6). In addition to the increase in capacity, Si is nontoxic, highly abundant, and inexpensive. Despite these advantages, the volumetric expansion of LixSi and poor electrical conductivity of Si makes developing a pure silicon anode with reasonable cycle life a seemingly insurmountable challenge. Composite electrodes of Si and C could represent the next-generation of Li-ion anodes for EVs. Hollow graphene nanoshells (HGNS) are a conductive graphitic carbon ~50 nm in diameter that can charge in minutes and have cycle lives of over 1000 cycles with minimal fade making them a promising support material for silicon nanostructures of higher capacity. Utilizing a facile low-temperature solution synthesis method, silicon was synthesized onto the HGNS to produce Si/HGNS composites in high yield and purity. The electrochemical performance of the composite material had a reversible capacity of ~3500 mAh/g Si (1400 mAh/g composite) after a C/20 formation cycle with 80% first cycle Coulombic efficiency. At an increased rate of C/2, a reversible capacity of ~2800 mAh/g Si (1100 mAh/g composite) is achieved with stable cycling performance. Utilizing this solution synthesis method, efficient mixing of Si with HGNS can produce Li-ion anode composites greater than 3 times the capacity of graphite with stable performance at charging rates required for upcoming EV powertrains.