## New strategy for enabling Li-metal anodes in high capacity batteries; trapping Li in microcages

##### 31 December 2017

Researchers in China are proposing a new strategy to retard dendrite formation on Li metal anodes in high-capacity Li-ion batteries. In a paper published in the ACS journal Nano Letters, they describe trapping Li within hollow silica microspheres with a carbon nanotube core to suppress dendrite growth.

Such an electrode exhibited a dendrite-free morphology after plating 2 mA h cm–2 of Li. Because the dendrite growth is suppressed, the as-obtained electrode maintains a high plating/stripping efficiency of 99% over 200 cycles.

… lithium metal batteries (LMBs) have received much attention because of their high energy density. In LMBs, the high specific capacity (3860 mA h g−1) and low electrochemical potential (−3.04 V vs standard hydrogen electrode) of Li metal hold promise for its use as an ideal anode material. However, dendrite formation induced by inhomogeneous deposition causes poor cycling efficiency and internal short circuiting, which further lead to battery failure and safety hazards. Since the dendrite issue severely impedes practical applications of LMBs, attempts must be made to address this fatal problem of Li metal anodes.

Recently, quite a few approaches, such as electrolyte additives, stable interfacial layers, and modified electrodes, have been proposed to resolve the critical issues of Li metal anodes. As one of the most efficient strategies, regulating Li deposition with an elegant structure was proven to be effective. … Although the heterogeneous structure plays a significant role in regulating the deposition behavior, the elaborate regulation mechanism of Li metal is restricted by the deposition conditions (i.e., deposition capacity and current density). Therefore, the heterogeneous structure needs to be improved to guide uniform deposition in the case of excess deposition capacity.

Herein we propose a heterogeneous structure with a conductive core and a porous insulative sheath for dendrite-free Li metal anodes. The heterogeneous structure shows two advantages: (i) the conductive core provides nucleation sites for initial Li deposition, and the porous insulative sheath guarantees enough Li ion flux and constrains Li deposition within the microcages; (ii) the uniform insulative coating layer prevents locally high electric field and guides uniform deposition on the electrode.

—Zuo et al.

The team designed a composite microcage with a carbon nanotube core and a porous silica sheath. Li metal is accommodated in the microcage, with the heterogeneous structure serving as a trapper.

 Illustration of the Li trapper in the electrochemical deposition process. (a) Schematic presentation of Li deposition into the microcage. (b) TEM image of the microcage after Li deposition. (c) TEM image of the Li-plated microcage after in situ electron beam irradiation. Credit: ACS, Zuo et al. Click to enlarge.

In their experiments, they found that the effective entrapment of Li metal guaranteed favorable deposition and excellent electrochemical performance.

We believe that the concept of trapping Li within the microcages can realize dendrite-free Li metal anodes and hasten the practical application of rechargeable Li metal batteries.

—Zuo et al.

Resources

• Tong-Tong Zuo, Ya-Xia Yin, Shu-Hua Wang, Peng-Fei Wang, Xinan Yang, Jian Liu, Chun-Peng Yang, and Yu-Guo Guo (2017) “Trapping Lithium into Hollow Silica Microspheres with a Carbon Nanotube Core for Dendrite-Free Lithium Metal Anodes” Nano Letters doi: 10.1021/acs.nanolett.7b04136

Will cost be below $100/KW when mass produced? With all the demand for Li batteries coming to market,$100 looks more like a wish and/or a hope. However, this could change with a break thru, perhaps with a new chemistry, i.e., NaS or solid state.