Reaction-Ball-Milling-Driven Surface Coating Strategy to Suppress Pulverization of Microparticle Si Anodes

In this work, we report a novel reaction-ball-milling surface coating strategy to suppress the pulverization of microparticle Si anodes upon lithiation/delithiation. By energetically milling the partially prelithiated microparticle Si in a CO₂ atmosphere, a multicomponent amorphous layer composed of SiO_<i>x</i>, C, SiC, and Li₂SiO₃ is successfully coated on the surface of Si microparticles. The coating level strongly depends on the milling reaction duration, and the 12 h milled prelithiated Si microparticles (BM12h) under a pressure of 3 bar of CO₂ exhibit a good conformal coating with 1.006 g cm^–3 of tap density. The presence of SiC remarkably enhances the mechanical properties of the SiO_<i>x</i>/C coating matrix with an approximately 4-fold increase in the elastic modulus and the hardness values, which effectively alleviates the global volume expansion of the Si microparticles upon lithiation. Simultaneously, the existence of Li₂SiO₃ insures the Li-ion conductivity of the coating layer. Moreover, the SEI film formed on the electrode surface maintains relatively stable upon cycling due to the remarkably suppressed crack and pulverization of particles. These processes work together to allow the BM12h sample to offer much better cycling stability, as its reversible capacity remains at 1439 mAh g^–1 at 100 mA g^–1 after 100 cycles, which is nearly 4 times that of the pristine Si microparticles (381 mAh g^–1). This work opens up new opportunities for the practical applications of micrometer-scale Si anodes

The Mechanism of Electrolyte Gating on High‑<i>T</i>_<i>c</i> Cuprates: The Role of Oxygen Migration and Electrostatics

Electrolyte gating is widely used to induce large carrier density modulation on solid surfaces to explore various properties. Most of past works have attributed the charge modulation to electrostatic field effect. However, some recent reports have argued that the electrolyte gating effect in VO₂, TiO₂, and SrTiO₃ originated from field-induced oxygen vacancy formation. This gives rise to a controversy about the gating mechanism, and it is therefore vital to reveal the relationship between the role of electrolyte gating and the intrinsic properties of materials. Here, we report entirely different mechanisms of electrolyte gating on two high-<i>T</i>_<i>c</i> cuprates, NdBa₂Cu₃O_7−δ (NBCO) and Pr_2–<i>x</i>Ce_<i>x</i>CuO₄ (PCCO), with different crystal structures. We show that field-induced oxygen vacancy formation in CuO chains of NBCO plays the dominant role, while it is mainly an electrostatic field effect in the case of PCCO. The possible reason is that NBCO has mobile oxygen in CuO chains, while PCCO does not. Our study helps clarify the controversy relating to the mechanism of electrolyte gating, leading to a better understanding of the role of oxygen electro migration which is very material specific