A team from Zhejiang A&F University, Huazhong University of Science and Technology (HUST), and Stanford University have developed a binder-free, flexible, and free-standing electrode comprising an unprecedented 92% silicon content for Li-ion batteries.

The structure shows an ultrahigh electrode-specific capacity of 2700 mAh g⁻¹, excellent cycling stability under a high silicon content of 85% (>2000 mAh g⁻¹ after 300 cycles) and a commercial-level areal capacity (5.58 mAh cm⁻²). A paper on the work is published in the RSC journal Energy & Environmental Science.

The development of lithium-ion batteries (LIBs) with a reduced weight, higher capacity, and longer service life is considered to be the most important strategy to address the critical needs of applications such as next-generation mobile electronics and electric vehicles. Silicon (Si) has received wide-spread attention as the most promising anode material for the next generation of LIBs because of its high theoretical specific capacity of 3579 mAh g⁻¹ (Li₁₅Si₄).

However, challenges arise owing to the large change in volume (>300%) under operation and poor electrical conductivity of Si, which significantly restricts the stability and kinetics process of the electrodes. In fact, to maintain electrode integrity, the industry has had to use a relatively low amount of Si (<15% in mass) in commercial anodes. Such a low Si content severely weakens the capacity advantage of silicon material in electrode level.

In this study, we designed a cellulose-based topological microscroll structure to achieve an unprecedented silicon content of 92% without any binder for the entire electrode, and investigated the use of it as a flexible, binder-free, and self-standing anode for LIBs.

—Wang et al.

In the Si@CNT/C-microscroll design, carbon-coated silicon nanoparticles are anchored on conductive carbon nanotubes and subsequently confined in cellulose carbon rolls with enough internal voids to accommodate the volume expansion of silicon; thus, a uniform dispersion of silicon with high reactivity is achieved.

Si@CNT/C-microscrolls design. (a) One microscroll before and after electrochemical cycling. (b) SEM image of a Si@CNT/C-microscroll. (c) SEM image of one microscroll. (d) Nitrogen adsorption–desorption isotherm with a pore-size distribution curve of the Si@CNT/C-microscrolls showing a good porosity (10–100 nm). Wang et al.

This strategy offers a new way to design electrodes with a high active material content for high performance batteries.

—Wang et al.

Resources

• Hanwei Wang, Jinzhou Fu, Chao Wang, Jiangyan Wang, Ankun Yang, Caicai Li, Qingfeng Sun, Yi Cui and Huiqiao Li (2020) “A binder-free high silicon content flexible anode for Li-ion batteries” Energy Environ. Sci. doi: 10.1039/C9EE02615K