Stoichiometry-Controlled Reversible Lithiation Capacity in Nanostructured Silicon Nitrides Enabled by in Situ Conversion Reaction

Abstract

In modern Li-based batteries, alloying anode materials have the potential to drastically improve the volumetric and specific energy storage capacity. For the past decade silicon has been viewed as a “Holy Grail” among these materials; however, severe stability issues limit its potential. Herein, we present amorphous substoichiometric silicon nitride (SiN x ) as a convertible anode material, which allows overcoming the stability challenges associated with common alloying materials. Such material can be synthesized in a form of nanoparticles with seamlessly tunable chemical composition and particle size and, therefore, be used for the preparation of anodes for Li-based batteries directly through conventional slurry processing. Such SiN x materials were found to be capable of delivering high capacity that is controlled by the initial chemical composition of the nanoparticles. They exhibit an exceptional cycling stability, largely maintaining structural integrity of the nanoparticles and the complete electrodes, thus delivering stable electrochemical performance over the course of 1000 charge/discharge cycles. Such stability is achieved through the in situ conversion reaction, which was herein unambiguously confirmed by pair distribution function analysis of cycled SiN x nanoparticles revealing that active silicon domains and a stabilizing Li2SiN2 phase are formed in situ during the initial lithiation.

Operando XRD studies on Bi2MoO6 as anode material for Na-ion batteries

“…A common degradation mechanism for alloying materials is particle fracturing and pulverization caused by large volume changes during cycling [30][31][32][33]. From the SEM images in this study (figure 5, S2 and S3), we do not observe any signs of cracking.…”

Enabling Increased Delithiation Rates in Silicon‐Based Anodes through Alloying with Phosphorus

“…The introduction of PH 3 gas into SiH 4 pyrolysis process resulted in the formation of SiP x NPs, where the ratio of Si : P is manipulated through control of the ratio of silane to phosphine gases supplied into the reactor during pyrolysis. This technique has been previously applied not only to produce Si nanoparticles, [31] but also to produce more complex SiN x (nano)particles with precise ratios of Si : N and controlled morphology and particle size [25] . The obtained materials were characterized using microscopy‐based methods, as the amorphous nature of the SiP x particles as well as the formation of a solid solution of P in Si limits the selection of characterization techniques.…”

“…Gradual capacity increases are observed in other literature, but the reason is not completely understood. [25,46] For P0, P1.5 and P3.2 the difference between the cycling and diagnostic cycles remains unchanged, indicating that the overpotential is constant. In contrast, the disparity between the cycling and diagnostic cycles in P5.2 is larger at later cycles, which implies that the overpotential increases over time.…”

Fe3+-Derived Boosted Charge Transfer in an FeSi4P4 Anode for Ultradurable Li-Ion Batteries

“…Therefore, these images lead to the inference that the low concentration of Fe 3+ in R-FSPC conspicuously changed the discharge products after only 30 cycles, unlike with the FSPC electrode. Further, Fe 2+ could not impart the catalytic properties to prevent the formation of the unwanted c-Li 3.75 Si and LiP phases, thereby causing large destructive stress on the R-FSPC electrode. − ,− This can directly alter the thickness, uniformity, morphology, and composition of the SEI film. Moreover, inadequate nanoscale diffusion owing to slow reaction kinetics negatively aggregated both electrochemically active and inactive materials during the lithiation process, thereby imposing undesirable stress on R-FSPC.…”

“…The formation of unfavorable c-Li 3.75 Si as the discharge product causes extreme volume expansion of the electrode and pulverizes it, thereby disconnecting the electrode materials from the Cu current collector and causing uncontrolled electrolyte decomposition. This results in the formation of a nonuniform solid-electrolyte interphase (SEI) layer, low CE, and rapid capacity decay. ,,− Therefore, manipulating the lithiation products to reach the a-Li 3.5 Si phase instead of c-Li 3.75 Si can preserve the integrity of an electrode over long cycles.…”