A team at Penn State has developed a three-dimensional, cross-linked polyethylenimine lithium-ion-affinity sponge as the lithium metal anode host to mitigate the problem of dendritic growth of the metal anode. A paper on their work is published in Nature Energy.

Using metals as anodes in metal batteries is considered as the most promising approach to achieve high energy density in next-generation batteries, and it is applied in commercial low-cost batteries such as zinc (Zn) metal batteries and lead acid batteries. However, the plating/stripping of metals is often compromised by metal dendritic growth, which leads to irreversible processes that reduce the Coulombic efficiency (CE) and deteriorates cycling performance. Using alkaline metal anodes, such as lithium (Li) and sodium (Na) poses a particular challenge because the metal deposition is associated with severe electrolyte decomposition due to the high reactivities of these metals, which promotes a non-uniform nucleation and the severe growth of mossy dendritic metal.

To date, considerable efforts, especially for Li metal anodes, have focused on the development of protective or interfacial layers, electrolyte additives to promote a durable solid–electrolyte interphase (SEI), alternative electrolytes and polymeric/lithiophilic anodic hosts. Although these methods assist in mitigating dendritic Li growth, it is still a challenge to achieve dendrite-free plating/ stripping of Li with high CEs at both the high current densities and high deposition capacities required to implement a high-energy and long-cycling life of Li metal batteries.

… Inspired by a variety of electrokinetic phenomena in porous media under an electric field that enable enhanced mass transport, such as electrokinetic surface conduction, electro-osmosis and electrophoresis, we developed a 3D polymeric porous sponge capable of providing Li-ion affinity and promoting electrokinetic phenomena.

—Li et al.

The team showed that electrokinetic surface conduction and electro-osmosis within the sponge change the concentration and current density profiles, which enables dendrite-free plating/stripping of lithium with a high Coulombic efficiency at high deposition capacities and current densities, even at low temperatures.

The use of a lithium-hosting sponge led to a significantly improved cycling stability of lithium metal batteries with a limited amount of lithium (for example, the areal lithium ratio of negative to positive electrodes is 0.6) at a commercial-level areal capacity.

The three-dimensional, cross-linked polymer sponge not only promotes ion transfer, but also inhibits deterioration.

The researchers also observed dendrite-free morphology in sodium and zinc anodes, indicating a broader promise of this approach.

The Li-ion electrokinetic self-concentrating and pumping effects of 3D PPS alter the Li deposition behaviour and enable a dendrite-free growth of Li metal at both high deposition capacities and high current densities and, in turn, extend the cycle life of high-areal-capacity Li metal batteries. This approach is shown to be applicable to various liquid electrolytes and can also resolve the dendritic issues of Li metal anodes at low temperatures.

—Li et al.

Looking to the future, the team will explore the practical applications in a large-format battery cell to demonstrate its advantages and feasibility.

The US Department of Energy funded this research.

Resources

• Guoxing Li, Zhe Liu, Qingquan Huang, Yue Gao, Michael Regula, Daiwei Wang, Long-Qing Chen & Donghai Wang (2018) “Stable metal battery anodes enabled by polyethylenimine sponge hosts by way of electrokinetic effects” Nature Energy doi: 10.1038/s41560-018-0276-z