Ion‐Conductive, Viscosity‐Tunable Hexagonal Boron Nitride Nanosheet Inks

Abstract

Liquid-phase exfoliation of layered solids holds promise for the scalable production of 2D nanosheets. When combined with suitable solvents and stabilizing polymers, the rheology of the resulting nanosheet dispersions can be tuned for a variety of additive manufacturing methods. While significant progress is made in the development of electrically conductive nanosheet inks, minimal effort is applied to ion-conductive nanosheet inks despite their central role in energy storage applications. Here, the formulation of viscosity-tunable hexagonal boron nitride (hBN) inks compatible with a wide range of printing methods that span the spectrum from low-viscosity inkjet printing to high-viscosity blade coating is demonstrated. The inks are prepared by liquid-phase exfoliation with ethyl cellulose as the polymer dispersant and stabilizer. Thermal annealing of the printed structures volatilizes the polymer, resulting in a porous microstructure and the formation of a nanoscale carbonaceous coating on the hBN nanosheets, which promotes high wettability to battery electrolytes. The final result is a printed hBN nanosheet film that possesses high ionic conductivity, chemical and thermal stability, and electrically insulating character, which are ideal characteristics for printable battery components such as separators. Indeed, lithium-ion battery cells based on printed hBN separators reveal enhanced electrochemical performance that exceeds commercial polymer separators.

On the relationship between morphology and conductivity in nanosheet networks

“…For example, due to its electronic conductivity, networks of liquid-exfoliated graphene nanosheets can be used as printed electrodes [16,27,34,35]. Conversely, due to their insulating nature BN networks can be used as ion conductors [16,36] or dielectrics [37]. Alternatively, the semiconducting nature of materials such as MoS 2 or WSe 2 has allowed their networks to be used as the active material in transistors [16,34,38].…”

Large-Area Thermal Distribution Sensor Based on Multilayer Graphene Ink

“…In addition to pursuing different deposition methods for the thermoelectric layer, alternative strategies for the realization of the dielectric layer could further improve the scalability of device fabrication. Potential candidates could include, for example, ink-based approaches comprising hexagonal boron nitride (hBN) [ 54 ] or flexible ion-gel dielectrics suitable for low-temperature fabrication, which have previously been exploited in conjunction with graphene [ 55 ].…”

Advances in Studies of Boron Nitride Nanosheets and Nanocomposites for Thermal Transport and Related Applications

“…There have been efforts on the use of surfactants, [54][55][56][57][58][59][60][61] polymers and biopolymers, [13,[62][63][64][65][66][67][68][69][70][71][72][73] and large aromatic molecules, [74][75][76][77][78][79] mostly in aqueous media, to improve the exfoliation. For example, sodium cholate and sodium deoxycholate surfactants were found to slightly improve the h-BN exfoliation in water with vigorous sonication, resulting in more concentrated and stable dispersions of exfoliated BNNs.…”

“…[57,60] Conceptually similar has been the use of polymers and biopolymers in water or organic solvents in the exfoliation processing. [19,[62][63][64][65][66][67][68][69][70][71][72][73] Among popular polymer choices have been polyvinylpyrrolidone (PVP), poly(vinyl alcohol), poly(styrene-bmethyl methacrylate), poloxamers, etc. [62][63][64][65][66][67][68][69][70][71][72][73] The idea behind the use of polymers was to explore the possible steric effect, such that the hydrophobic groups of the polymer are partially adsorbed onto the basal plane of h-BN via πÀ π, hydrophobic, van der Waals, or charge transfer interactions, and at the same time, the hydrophilic groups are projected into the aqueous medium to provide effective repulsion.…”