Friday, July 21, 2017

Two New Approaches to High-Performance Long-Lasting SiOx Li-Ion Batteries

Improved cyclic performance and excellent rate capability (Credit: Click to Enlarge.
Although silicon is a very attractive anode material because of its higher energy density, its huge volume change over repeated charge−discharge cycles rapidly degrades cycle life.  As an alternative approach to mitigate the well-known drawbacks of silicon while retaining the energy density advantages, silicon monoxide (SiOx, x ≈ 1) has become attractive as well.

SiOx offers high reversible specific capacity and improved cyclic performance; however, it still suffers from inevitable volumetric changes and poor electrical conductivity.  A number of research efforts have tackled those challenges as well.  Now, separate research teams in China and the US report two new approaches toward a commercially viable SiOx electrode.
  • High performance SiOx anode is obtained by simple high-energy ball-milling method.
  • Size-reduced SiOx with amorphous component suppresses the volume changes effectively.
  • Optimized conductive agents provide super electrical conductivity.
A team at the University of Kentucky (Chen et al.) has synthesized a high performance binder-free SiOx/C composite electrode for Li-ion batteries by mixing SiOx particles and Kraft lignin.  After a heat treatment, the lignin formed a conductive matrix hosting SiOx particles, ensuring electronic conductivity, connectivity, and accommodation of volume changes during lithiation/delithiation.  No conventional binder or conductive agent was necessary.

The composite electrode showed excellent performance, maintaining ∼900 mAh g−1 after 250 cycles at a rate of 200 mA g−1, and good rate capability.

They attributed the excellent electrochemical performance to the comparatively small volume change of SiOx-based electrodes (160%) and the flexibility of the lignin-derived carbon matrix to accommodate the volume change.  A paper on their work is published in the Journal of Power Sources.

The team in China (Zhang et al.) developed a mild and efficient method to prepare a micro-sized SiOx/C core–shell composite.  By mixing citric acid and ball-milled SiOx and subjecting them to carbonization, they obtained a uniform SiOx/C core–shell composite with a micro-sized SiOx core and conformal carbon shell.

The carbon shell effectively enhanced the electrical conductivity of SiOx and mitigated the volume changes of SiOx during lithiation and delithiation.  The SiOx/C composite electrode delivered a reversible specific capacity of 1296.3 mAh g–1; coulombic efficiency of as high as 99.8%; and capacity retention of 65.1% (843.5 mAh g–1) after 200 cycles.

The composite also exhibited excellent rate capability.  The approach is mild, mass-productive, and cost-effective and, thus, can be employed in large-scale production of high-performance SiOx/C composite anode material, the team said.  A paper on their work is published in the ACS journal Energy & Fuels.

Read more at Two New Approaches to High-Performance SiOx Anodes for Li-Ion Batteries

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