Composition dependent electrochemical properties of earth-abundant ternary nitride anodes

Growing energy storage demands on lithium-ion batteries necessitate exploration of new electrochemical materials as next-generation battery electrode materials. In this work, we investigate the previously unexplored electrochemical properties of earth-abundant and tunable Zn1-xSn1+xN2 (x = -0.4 to x = 0.4) thin films, which show high electrical conductivity and high gravimetric capacity for Li insertion. Enhanced cycling performance is achieved compared to previously published end-members Zn3N2 and Sn3N4, showing decreased irreversible loss and increased total capacity and cycle stability. The average reversible capacity observed is > 1050 mAh/g for all compositions and 1220 mAh/g for Zn-poor (x = 0.2) films. Extremely Zn-rich films (x = -0.4) show improved adhesion; however, Zn-rich films undergo a phase transformation on the first cycle. Zn-poor and stoichiometric films do not exhibit significant phase transformations which often plague nitride materials and show no required overpotential at the 0.5 V plateau. Cation composition x is explored as a mechanism for tuning relevant mechanical and electrochemical properties, such as capacity, overpotential, phase transformation, electrical conductivity, and adhesion. The lithiation/delithiation experiments confirm the reversible electrochemical reactions. Without any binding additives, the as-deposited electrodes delaminate resulting in fast capacity degradation. We demonstrate the mechanical nature of this degradation through decreased electrode thinning, resulting in cells with improved cycling stability due to increased mechanical stability. Combining composition and electrochemical analysis, this work demonstrates for the first time composition dependent electrochemical properties for the ternary Zn1-xSn1+xN2 and proposes earth-abundant ternary nitride anodes for increased reversible capacity and cycling stability

A Proposed General Solution for Li Dendrite Penetration into Solid Electrolytes

We propose a general solution to the problem of Li dendrite penetration through solid electrolytes such as LLZO. The solution is based on an analogy of Li dendrite penetration to stress corrosion cracking, a process in which a very soft material--water--penetrates through a very hard material--steel--generally at grain boundaries. The problem of stress corrosion cracking was solved many years ago by putting the surface into a state of residual compressive stress. A variety of materials have been strengthened this way, including metals, glasses (e.g., Gorilla glass), and ceramics. However, for this approach to be useful, it is critical, at a minimum, that the presence of a significant residual compressive stress not block ion transport. In this work, we used DFT to show that isotropic compressive residual stresses as high as -10 GPa—the maximum observed in strengthened ceramics—have only a minimal impact on the diffusion rate of Li+ ions through a near-surface region of LLZO. Figure

DataSheet1_An electronically conductive 3D architecture with controlled porosity for LiFePO4 cathodes.docx

Thick LiFePO4 (LFP) cathodes offer a promising solution to increasing the areal capacity and reducing the cost of Li-ion batteries while retaining the qualities intrinsic to LFP, including long cycle lifetimes and thermal stability required for electric vehicles and stationary energy storage applications. However, the primary challenges of thick LFP cathodes are poor rate capability and cycling stability due to LFP’s electronically insulating material property, poor electronic conductivity, and long diffusion length at high electrode thicknesses. Herein, we propose an electrode architecture composed of vertically aligned carbon fibers (CFs) attached to a plasticized current collector (PCC) to promote rate capability, cycle life, and further enhance the safety of thick LFP cathodes. The effectiveness of the CF-PCC architecture is demonstrated by electrochemical analysis with a good areal capacity of 3.5 mA cm-2, excellent cycling stability at C/3, and good rate capability up to 1C. These results are confirmed by investigating the architecture’s impact on ionic diffusivity via electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) compared to the conventional slurry cast LFP cathode.</p

Origin of Bonding between the SWCNT and the Fe₃O₄(001) Surface and the Enhanced Electrical Conductivity

Recent experiments have demonstrated that adding single-wall carbon nanotubes (SWCNTs) to Fe₃O₄ nanoparticle electrodes leads to dramatically improved electrical conductivity and performance of Li ion batteries. Our density functional theory (DFT) calculations reveal that the interactions between both pristine and B- or N-doped SWCNTs and the Fe₃O₄(001) surface are very weak. Although C vacancies in SWCNTs can lead to stronger chemical bonding between SWCNTs and Fe₃O₄(001) surfaces, the binding and electrical conductivity in this case are not ideal. Interestingly, we show that transition-metal (Fe, Ni) atoms or clusters facilitate the formation of strong chemical bonding between SWCNTs and Fe₃O₄(001) surfaces, providing excellent channels for electrons flowing between SWCNTs and Fe₃O₄(001) surfaces, which is essential for improving electrical conductivity of the mixed electrodes. The calculated electron conductance of the transition-metal-decorated system is improved by more than 2 orders of magnitude, in agreement with experimental observations. Our results, therefore, suggest a viable way for functionalizing SWCNTs

Systematic Investigation of the Alucone-Coating Enhancement on Silicon Anodes

Polyvinylidene fluoride (PVDF) is the most popular binder in commercial lithium-ion batteries but is incompatible with a silicon (Si) anode because it fails to maintain the mechanical integrity of the Si electrode upon cycling. Herein, an alucone coating synthesized by molecular layer deposition has been applied on the laminated electrode fabricated with PVDF to systematically study the sole impact of the surface modification on the electrochemical and mechanical properties of the Si electrode, without the interference of other functional polymer binders. The enhanced mechanical properties of the coated electrodes, confirmed by mechanical characterization, can help accommodate the repeated volume fluctuations, preserve the electrode structure during electrochemical reactions, and thereby, leading to a remarkable improvement of the electrochemical performance. Owing to the alucone coating, the Si electrodes achieve highly reversible cycling performance with a specific capacity of 1490 mA h g^–1 (0.90 mA h cm^–2) as compared to 550 mA h g^–1 (0.19 mA h cm^–2) observed in the uncoated Si electrode. This research elucidates the important role of surface modification in stabilizing the cycling performance and enabling a high level of material utilization at high mass loading. It also provides insights for the future development of Si anodes