Integrating SEI into Layered Conductive Polymer Coatings for Ultrastable Silicon Anodes.

Tackling the huge volume expansion of silicon (Si) anode desires a stable solid electrolyte interphase (SEI) to prohibit the interfacial side reactions. Here, a layered conductive polyaniline (LCP) coating is built on Si nanoparticles to achieve high areal capacity and long lifespan. The conformal LCP coating stores electrolyte in interlamination spaces and directs an in situ formation of LCP-integrated hybrid SEI skin with uniform distribution of organic and inorganic components, enhancing the flexibility of the SEI to buffer the volume changes and maintaining homogeneous ion transport during cycling. As a result, the Si anode shows a remarkable cycling stability under high areal capacity (≈3 mAh cm-2 ) after 150 cycles and good rate performance of 942 mAh g-1 at 5 A g-1 . This work demonstrates the great potential of regulating the SEI properties by a layered polymer-directing SEI formation for the mechanical and electrochemical stabilization of Si anodes.

1000 Wh L-1 lithium-ion batteries enabled by crosslink-shrunk tough carbon encapsulated silicon microparticle anodes.

Microparticulate silicon (Si), normally shelled with carbons, features higher tap density and less interfacial side reactions compared to its nanosized counterpart, showing great potential to be applied as high-energy lithium-ion battery anodes. However, localized high stress generated during fabrication and particularly, under operating, could induce cracking of carbon shells and release pulverized nanoparticles, significantly deteriorating its electrochemical performance. Here we design a strong yet ductile carbon cage from an easily processing capillary shrinkage of graphene hydrogel followed by precise tailoring of inner voids. Such a structure, analog to the stable structure of plant cells, presents 'imperfection-tolerance' to volume variation of irregular Si microparticles, maintaining the electrode integrity over 1000 cycles with Coulombic efficiency over 99.5%. This design enables the use of a dense and thick (3 mAh cm-2) microparticulate Si anode with an ultra-high volumetric energy density of 1048 Wh L-1 achieved at pouch full-cell level coupled with a LiNi0.8Co0.1Mn0.1O2 cathode.

A thick yet dense silicon anode with enhanced interface stability in lithium storage evidenced by in situ TEM observations.

Increasing the density and thickness of electrodes is required to maximize the volumetric energy density of lithium-ion batteries for practical applications. However, dense and thick electrodes, especially high-mass-content (>50 wt%) silicon anodes, have poor mechanical stability due to the presence of a large number of unstable interfaces between the silicon and conducting components during cycling. Here we report a network of mechanically robust carbon cages produced by the capillary shrinkage of graphene hydrogels that can contain the silicon nanoparticles in the cages and stabilize the silicon/carbon interfaces. In situ transmission electron microscope characterizations including compression and tearing of the structure and lithiation-induced silicon expansion experiments, have provided insight into the excellent confinement and buffering ability of this interface-strengthened graphene-caged silicon nanoparticle anode material. Consequently, a dense and thick silicon anode with reduced thickness fluctuations has been shown to deliver both high volumetric (>1000 mAh cm-3) and areal (>6 mAh cm-2) capacities together with excellent cycling capability.