A team at Harvard has a developed a design for a solid-state battery that uses a hierarchy of interface stabilities (to lithium metal responses), to achieve an ultrahigh current density with no lithium dendrite penetration.

Cycling performance of the Li-metal anode paired with a LiNi_0.8Mn_0.1Co_0.1O₂ cathode is very stable, with an 82% capacity retention after 10,000 cycles at a 20C rate, and 81.3% capacity retention after 2,000 cycles at a 1.5C rate.

The design also enables a specific power of 110.6 kW/kg and specific energy up to 631.1 Wh/kg at the micrometer-sized cathode material level. A paper on the work is published in the journal Nature.

A major challenge with Li-metal batteries (in which the anode is made of lithium metal) is dendrite formation on the surface of the anode. These needle-like structures grow into the electrolyte and pierce the separator, causing the battery to short or catch fire.

Although solid-state electrolytes are expected to suppress dendrite formation, micrometer- or submicrometer-sized cracks in ceramic pellets can frequently be generated during battery assembly or long-time cycling. Once cracks form, lithium dendrite penetration is inevitable, the researchers said.

To overcome this challenge, Li and his team designed a multilayer battery that sandwiches different materials of varying stabilities between the anode and cathode. This multilayer, multimaterial battery prevents the penetration of lithium dendrites not by stopping them altogether but rather by controlling and containing them.

Our multilayer design has the structure of a less-stable electrolyte sandwiched between more-stable solid electrolytes, which prevents any lithium dendrite growth through well localized decompositions in the less stable electrolyte layer. A mechanism analogous to the expansion screw effect is proposed, whereby any cracks are filled by dynamically generated decompositions that are also well constrained, probably by the ‘anchoring’ effect the decompositions induce.

—Ye and Li

The first electrolyte (Li_5.5PS_4.5Cl_1.5, LPSCI) is more stable with lithium but prone to dendrite penetration. The second electrolyte, (Li₁₀Ge₁P₂S₁₂, LGPS) is less stable with lithium but appears immune to dendrites.

In this design, dendrites are allowed to grow through the graphite and first electrolyte but are stopped when they reach the second.

The battery is also self-healing; its chemistry allows it to backfill holes created by the dendrites.

This proof-of-concept design shows that lithium-metal solid-state batteries could be competitive with commercial lithium-ion batteries. And the flexibility and versatility of our multilayer design makes it potentially compatible with mass production procedures in the battery industry. Scaling it up to the commercial battery won’t be easy and there are still some practical challenges, but we believe they will be overcome.

—Xin Li, corresponding author

Resources

• Ye, L., Li, X. (2021) “A dynamic stability design strategy for lithium metal solid state batteries.” Nature 593, 218–222 doi: 10.1038/s41586-021-03486-3