Browsing by Author "Xu, Wei"

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Biochar as a Renewable Substitute for Carbon Black in Lithium-Ion Battery Electrodes
(American Chemical Society, 2022-09) Kane, Seth; Storer, Aksiin; Xu, Wei; Ryan, Cecily; Stadie, Nicholas P.
Lignin-derived biochar was prepared and characterized towards potential applications as a conductive electrode additive and active lithium host material within lithium-ion batteries (LIBs). This biochar was specifically selected for its high electrical conductivity, which is comparable to that of common conductive carbon black standards (e.g., Super P). Owing to its high electrical conductivity, this biochar serves as an effective conductive additive within electrodes comprised of graphite as the active material, demonstrating slightly improved cell efficiency and rate capability over electrodes using carbon black as the additive. Despite its effectiveness as a conductive additive in LIB anodes, preliminary results show that the biochar developed in this work is not suitable as a direct replacement for carbon black as a conductive additive in LiFePO4 (LFP) cathodes. This latter insufficiency may be due to differences in particle 2 geometry between biochar and carbon black; further optimization is necessary to permit the application of biochar as a general-purpose conductive additive in LIBs. Nevertheless, these investigations combined with an assessment of greenhouse gas emissions from biochar production show that replacing carbon black with biochar can be an effective method to improve the sustainability of LIBs.
Biochar as a Renewable Substitute for Carbon Black in Lithium-Ion Battery Electrodes
(American Chemical Society, 2022-09) Kane, Seth; Storer, Aksiin; Xu, Wei; Ryan, Cecily; Stadie, Nicholas P.
Lignin-derived biochar was prepared and characterized toward potential applications as a conductive electrode additive and active lithium host material within lithium-ion batteries (LIBs). This biochar was specifically selected for its high electrical conductivity, which is comparable to that of common conductive carbon black standards (e.g., Super P). Owing to its high electrical conductivity, this biochar serves as an effective conductive additive within electrodes comprising graphite as the active material, demonstrating slightly improved cell efficiency and rate capability over those of electrodes using carbon black as the additive. Despite its effectiveness as a conductive additive in LIB anodes, preliminary results show that the biochar developed in this work is not suitable as a direct replacement for carbon black as a conductive additive in LiFePO4 cathodes. This latter insufficiency may be due to differences in particle geometry between biochar and carbon black; further optimization is necessary to permit the application of biochar as a general-purpose conductive additive in LIBs. Nevertheless, these investigations combined with an assessment of greenhouse gas emissions from biochar production show that replacing carbon black with biochar can be an effective method to improve the sustainability of LIBs.
Exploring the Limits of the Rapid-Charging Performance of Graphite as the Anode in Lithium-Ion Batteries
(The Electrochemical Society, 2022-01) Xu, Wei; Welty, Connor; Peterson, Margaret R.; Read, Jeffrey A.; Stadie, Nicholas P.
Graphite is, in principle, applicable as a high-power anode in lithium-ion batteries (LIBs) given its high intralayer lithium diffusivity at room temperature. However, such cells are known to exhibit poor capacity retention and/or undergo irreversible side reactions including lithium plating when charged at current rates above ∼2 C (∼740 mA g−1). To explore the inherent materials properties that limit graphite anodes in rapid-charge applications, a series of full-cells consisting of graphite as the anode and a standard Li[Ni0.8Mn0.1Co0.1]O2 (NMC811) cathode was investigated. Instead of a conventional cathode-limited cell design, an anode-limited approach was used in this work to ensure that the overall cell capacity is only determined by the graphite electrode of interest. The optimized N:P capacity ratio was determined as N/P = 0.67, enabling stable cycling across a wide range of charging rates (4–20 C) without inhibition by the NMC811 cathode. The results show that unmodified, highly crystalline graphite can be an excellent anode for rapid-charge applications at up to 8 C, even with a standard electrolyte and NMC811 cathode and in cells with 1.0 mAh cm−2 loadings. As a rule, capacity and specific energy are inversely proportional to crystallite size at high rates; performance can likely be improved by electrolyte/cathode tuning.
Hydrogen-Type Binding Sites in Carbonaceous Electrodes for Rapid Lithium Insertion
(American Chemical Society, 2023-08) McGlamery, Devin; McDaniel, Charles; Xu, Wei; Stadie, Nicholas P.
Direct pyrolysis of coronene at 800 °C produces low-surface-area, nanocrystalline graphitic carbon containing a uniquely high content of a class of lithium binding sites referred to herein as “hydrogen-type” sites. Correspondingly, this material exhibits a distinct redox couple under electrochemical lithiation that is characterized as intermediate-strength, capacitive lithium binding, centered at ∼0.5 V vs Li/Li+. Lithiation of hydrogen-type sites is reversible and electrochemically distinct from capacitive lithium adsorption and from intercalation-type binding between graphitic layers. Hydrogen-type site lithiation can be fully retained even up to ultrafast current rates (e.g., 15 A g–1, ∼40 C) where intercalation is severely hampered by ion desolvation kinetics; at the same time, the bulk nature of these sites does not require a large surface area, and only minimal electrolyte decomposition occurs during the first charge/discharge cycle, making coronene-derived carbon an exceptional candidate for high-energy-density battery applications.
Stabilizing Effects of Phosphorus-Doped Silicon Nanoparticle Anodes in Lithium-Ion Batteries
(ACS Publications, 2023-01) Gordon, Isabelle P.; Xu, Wei; Randak, Sophia; Jow, T. Richard; Stadie, Nicholas P.
Phosphorus-doped silicon has been reported to exhibit improved cycling stability and/or higher capacity retention than pure silicon as the anode in lithium-ion batteries. However, crystallite size and particle morphology are difficult to decouple from compositional tuning during chemical modification. In this work, we explore direct solid-state routes to phosphorus doping of silicon powders relevant to electrochemical applications. A wide range of compositions are assessed, from 0.05 to 3.0 at % P, as well as a wide range of silicon starting materials of varying crystallinity, particle size, and particle morphology. Successful incorporation of phosphorus into the silicon lattice is best confirmed by X-ray diffraction; the Si(111) reflection shifts to higher angles as consistent with the known lattice contraction of 0.002 Å per 1 at % phosphorus. The addition of phosphorus to Si nanoparticles (100–500 nm) in the high doping regime causes grain coarsening and catalyzes an increase in crystallinity. On the other hand, dilute doping of phosphorus can be carried out without great alteration of the nanoparticulate morphology. The opposite effect occurs for very large microparticles (>10 μm), whereby the doping is concomitant with a disruption of the crystal lattice and reduction of the crystallite size. These effects are borne out in both the electrochemical stability over long-term cycling in a lithium-ion half-cell as well as in the thermal stability under high-temperature decomposition. By comparison across a wide range of pure and P-doped materials of varying particle and crystallite sizes, the independent effects of doping and structure on thermal and electrochemical stability are able to be decoupled herein. A stabilizing effect is most significant when phosphorus doping is dilute and heterogeneous (surface-enriched) within the silicon nanoparticles.