Alexandre Magasinski

High-performance lithium-ion anodes using a hierarchical bottom-up approach.

Si-based Li-ion battery anodes have recently received great attention, as they offer specific capacity an order of magnitude beyond that of conventional graphite. The applications of this transformative technology require synthesis routes capable of producing safe and easy-to-handle anode particles with low volume changes and stable performance during battery operation. Herein, we report a large-scale hierarchical bottom-up assembly route for the formation of Si on the nanoscale--containing rigid and robust spheres with irregular channels for rapid access of Li ions into the particle bulk. Large Si volume changes on Li insertion and extraction are accommodated by the particles internal porosity. Reversible capacities over five times higher than that of the state-of-the-art anodes (1,950 mA h g(-1)) and stable performance are attained. The synthesis process is simple, low-cost, safe and broadly applicable, providing new avenues for the rational engineering of electrode materials with enhanced conductivity and power.

A Major Constituent of Brown Algae for Use in High-Capacity Li-Ion Batteries

Alginate extracts help stabilize silicon nanoparticles used in a high-capacity lithium-silicon battery. The identification of similarities in the material requirements for applications of interest and those of living organisms provides opportunities to use renewable natural resources to develop better materials and design better devices. In our work, we harness this strategy to build high-capacity silicon (Si) nanopowder–based lithium (Li)–ion batteries with improved performance characteristics. Si offers more than one order of magnitude higher capacity than graphite, but it exhibits dramatic volume changes during electrochemical alloying and de-alloying with Li, which typically leads to rapid anode degradation. We show that mixing Si nanopowder with alginate, a natural polysaccharide extracted from brown algae, yields a stable battery anode possessing reversible capacity eight times higher than that of the state-of-the-art graphitic anodes.

Toward Efficient Binders for Li-Ion Battery Si-Based Anodes: Polyacrylic Acid

Si-based Li-ion battery anodes offer specific capacity an order of magnitude beyond that of conventional graphite. However, the formation of stable Si anodes is a challenge because of significant volume changes occurring during their electrochemical alloying and dealloying with Li. Binder selection and optimization may allow significant improvements in the stability of Si-based anodes. Most studies of Si anodes have involved the use of carboxymethylcellulose (CMC) and poly(vinylidene fluoride) (PVDF) binders. Herein, we show for the first time that pure poly(acrylic acid) (PAA), possessing certain mechanical properties comparable to those of CMC but containing a higher concentration of carboxylic functional groups, may offer superior performance as a binder for Si anodes. We further show the positive impact of carbon coating on the stability of the anode. The carbon-coated Si nanopowder anodes, tested between 0.01 and 1 V vs Li/Li+ and containing as little as 15 wt % of PAA, showed excellent stability during the first hundred cycles. The results obtained open new avenues to explore a novel series of binders from the polyvinyl acids (PVA) family.

Sulfur‐Infiltrated Micro‐ and Mesoporous Silicon Carbide‐Derived Carbon Cathode for High‐Performance Lithium Sulfur Batteries

Novel nanostructured sulfur (S)-carbide derived carbon (CDC) composites with ordered mesopores and high S content are successfully prepared for lithium sulfur batteries. The tunable pore-size distribution and high pore volume of CDC allow for an excellent electrochemical performance of the composites at high current densities. A higher electrolyte molarity is found to enhance the capacity utilization dramatically and reduce S dissolution in S-CDC composite cathodes during cycling.

Towards Ultrathick Battery Electrodes: Aligned Carbon Nanotube – Enabled Architecture

Vapor deposition techniques were utilized to synthesize very thick (∼1 mm) Li-ion battery anodes consisting of vertically aligned carbon nanotubes coated with silicon and carbon. The produced anode demonstrated ultrahigh thermal (>400 W·m(-1) ·K(-1)) and high electrical (>20 S·m(-1)) conductivities, high cycle stability, and high average capacity (>3000 mAh·g(Si) (-1)). The processes utilized allow for the conformal deposition of other materials, thus making it a promising architecture for the development of Li-ion anodes and cathodes with greatly enhanced electrical and thermal conductivities.

Sulfur-containing activated carbons with greatly reduced content of bottle neck pores for double-layer capacitors: a case study for pseudocapacitance detection

Synthesis of S-doped activated carbons (ACs) by carbonization and simultaneous activation of S-based polymers was found to be an efficient route to produce porous carbons for double layer capacitors (EDLCs) with high specific energy and power densities combined with low self-discharge. Here we investigate for the first time the processing-structure–property relationships related to the formation of polythiophene-derived ACs for EDLC applications. Sulfide bridges present in the polymer precursor were found to depress the shrinkage of the smallest micropores during the carbonization process and allow for the enhanced ion transport within the produced AC electrodes. The cyclic voltammetry (CV) measurements on S-doped ACs produced at 800 and 850 °C showed high specific capacitance (up to ∼200 F g−1) and no significant self-discharge in neutral aqueous electrolytes. More importantly, these capacitance values remained virtually identical for a sweep rate increasing from 1 to 50 mV s−1. The observed capacitance retention is quite remarkable for thick electrodes of ∼200 μm and a large AC particle size of 10–100 μm. It indicates great potential of the proposed synthesis technology for EDLCs operating at high frequencies and high currents. In the course of our systematic studies of AC performance in different electrolytes we found a strong correlation between the large pseudocapacitance and the significant self-discharge in ACs. We harness the difference between the characteristic times required to establish a double layer and that of the pseudocapacitive redox reactions and propose a simple method to estimate the fraction of pseudocapacitance. The proposed method is particularly valuable in cases when CV measurements do not show clear characteristic reduction–oxidation peaks.

Nanoporous Li2S and MWCNT-linked Li2S powder cathodes for lithium-sulfur and lithium-ion battery chemistries

In order to achieve high capacity utilization and high rate performance of lithium sulfide (Li2S) cathode materials, it is critical to identify scalable methods for low-cost preparation of nanostructured Li2S or Li2S-carbon composites. Here, we report on the preparation and characterization of nanoporous Li2S and multiwalled (MW) carbon nanotube (CNT) – linked Li2S powders, prepared for the first time via a versatile solution-based method. The addition of MWCNTs enhances electrical conductivity and structural stability of the Li2S-based cathodes and reduces polarization of cells operating at high current densities. The nanostructured Li2S-based cathodes containing 20 wt% MWCNT showed promising discharge capacities of up to ∼1050 mA h g−1S at a slow rate of C/20 and ∼800 mA h g−1S at a C/2 rate. Quite remarkably, without any electrolyte additives (such as polysulfides or lithium nitrate) MWCNT-linked Li2S cathodes demonstrated up to ∼90% capacity retention after 100 cycles in half cells (vs. Li foil) at a C/5 and C/10 rates.

Analysis of Lithium Insertion/Deinsertion in a Silicon Electrode Particle at Room Temperature

The dependence of the open-circuit potential on the state of charge in lithium insertion electrodes is usually measured at equilibrium conditions. For the modeling of lithium-silicon electrodes at room temperature, the use of a pseudo-thermodynamic potential vs composition curve based on metastable amorphous phase transitions with path dependence is proposed. Volume changes during lithium insertion/deinsertion in a single silicon electrode particle under potentiodynamic control are modeled and compared with experiments to provide justification for the same. Only if asymmetric transfer coefficients and sluggish kinetics are experimentally observed can kinetic hysteresis be reasoned for the potential gap in Li-Si system. The particle model enables one to analyze the influence of diffusion in the solid phase, particle size, and kinetic parameters without interference from other components in a practical porous electrode. Concentration profiles within the electrode particle under galvanostatic control are investigated. Sluggish kinetics is established from cyclic voltammograms at different scan rates. This work stresses the need for accurate experimental determination of kinetic parameters (and thus the exchange current density) in silicon nanoparticles. This model and knowledge thereof can be used in the cell-sandwich model for the design of lithium-ion cells with composite silicon negative electrodes.

Chemical Vapor Deposition of Aluminum Nanowires on Metal Substrates for Electrical Energy Storage Applications

Metal nanowires show promise in a broad range of applications, but many synthesis techniques require complex methodologies. We have developed a method for depositing patterned aluminum nanowires (Al NWs) onto Cu, Ni, and stainless steel substrates using low-pressure decomposition of trimethylamine alane complex. The NWs exhibited an average diameter in the range from 45 to 85 nm, were crystalline, and did not contain a detectable amount of carbon impurities. Atomic layer deposition of 50 nm of vanadium oxide on the surface of Al NW allows fabrication of supercapacitor electrodes with volumetric capacitance in excess of 1400 F·cc(-3), which exceeds the capacitance of traditional activated carbon supercapacitor electrodes by more than an order of magnitude.

In situ small angle neutron scattering revealing ion sorption in microporous carbon electrical double layer capacitors.

Experimental studies showed the impact of the electrolyte solvents on both the ion transport and the specific capacitance of microporous carbons. However, the related structure-property relationships remain largely unclear and the reported results are inconsistent. The details of the interactions of the charged carbon pore walls with electrolyte ions and solvent molecules at a subnanometer scale are still largely unknown. Here for the first time we utilize in situ small angle neutron scattering (SANS) to reveal the electroadsorption of organic electrolyte ions in carbon pores of different sizes. A 1 M solution of tetraethylammonium tetrafluoroborate (TEATFB) salt in deuterated acetonitrile (d-AN) was used in an activated carbon with the pore size distribution similar to that of the carbons used in commercial double layer capacitors. In spite of the incomplete wetting of the smallest carbon pores by the d-AN, we observed enhanced ion sorption in subnanometer pores under the applied potential. Such results suggest the visible impact of electrowetting phenomena counterbalancing the high energy of the carbon/electrolyte interface in small pores. This behavior may explain the characteristic butterfly wing shape of the cyclic voltammetry curve that demonstrates higher specific capacitance at higher applied potentials, when the smallest pores become more accessible to electrolyte. Our study outlines a general methodology for studying various organic salts-solvent-carbon combinations.