# Porous Structuring of Si Microparticles for Li-Ion Battery Anodes by Urea-Assisted Etching

## TL;DR

This paper introduces a new method to create porous silicon particles for lithium-ion batteries, improving performance and stability.

## Contribution

A urea-assisted etching method is introduced to create porous silicon microparticles without using HF, enabling better battery performance.

## Key findings

- Porous silicon microparticles with mesoporosity and surface functionalities were successfully produced using urea-assisted etching.
- Composite electrodes with 10–20 wt % porous silicon showed stable redox activity and retained 630–880 mAh g–1 after 100 cycles.
- Higher silicon loadings led to rapid capacity decay, but lower loadings maintained good Coulombic efficiency and rate capability.

## Abstract

Silicon-based anodes offer substantially higher theoretical
capacities
than graphite in lithium-ion batteries, but their practical deployment
is hindered by severe volume changes that induce mechanical degradation
and unstable interfacial chemistry. While nanoscaling strategies can
mitigate these effects, they often suffer from low tapped density,
complex synthesis, and limited scalability. Porous silicon microparticles
provide a promising alternative by partially accommodating volume
expansion while preserving processability and electrode-level integrity.
Here, a HF-free urea-assisted etching strategy is employed to generate
porous silicon microparticles under mild conditions, leveraging the
coupled action of thermally induced structural disruption and chemically
driven surface modification. Control experiments confirm that the
combined action of these effects is essential to achieve BJH-resolved
mesoporosity and increased surface area. The resulting porous silicon
exhibits oxygen- and nitrogen-containing surface functionalities.
Composite electrodes prepared with nanographite and sodium alginate
binder at graphite:silicon:binder ratios of 8:1:1, 7:2:1, and 4.5:4.5:1
demonstrate improved electrochemical behavior. In half-cell testing,
electrodes containing 10–20 wt % porous silicon deliver stable
redox activity and retain 630–880 mAh g–1 after 100 cycles at 0.1 C, with Coulombic efficiencies of 98.8–99.7%,
whereas higher silicon loadings lead to rapid capacity decay. Cycling-resolved
impedance and differential-capacity analyses reveal the formation
of a thicker yet mechanically resilient interphase that stabilizes
charge-transfer kinetics, while rate capability tests show 65–74%
capacity retention at 2 C.