Researchers at the Université catholique de Louvain in Belgium have designed and synthesized a new class of electrically conducting anionic coordination polymers for all practically relevant alkali-cation storage. Coordination compounds are molecules that possess a metal center bound to ligands (atoms, ions or molecules that donate electrons to the metal); these complexes can be neutral or charged.

The working voltage of these new chemistries is higher by nearly 1 V than state-of-the-art organic or coordination polymer chemistries, reaching values of 2.9–3.5 V in lithium-, sodium-, or potassium-based cells.

The phases are insoluble in battery electrolytes, have high gravimetric density, and can be cycled with low carbon content and high mass loading. An open-access paper on their work is published in the RSC journal Energy & Environmental Science.

Design principle and synthesis route of the alkali-ion contained coordination polymers with the general formula of A₂-TM-PTtSA, wherein: A = Li⁺, Na⁺, K⁺; TM = Fe²⁺, Co²⁺, Mn²⁺, and PTtSA = benzene-1,2,4,5-tetra-methylsulfonamide. Wang et al.

Coordination polymers (CPs) made of redox-active organic moieties and metal ions emerge as an important class of electroactive materials for battery applications. However, the design and synthesis of high voltage alkali-cation reservoir anionic CPs remains challenging, hindering their practical applications.

Herein, we report a family of electrically conducting alkali-cation reservoir CPs with the general formula of A₂-TM-PTtSA (wherein A = Li⁺, Na⁺, or K⁺; TM = Fe²⁺, Co²⁺, or Mn²⁺; and PTtSA = benzene-1,2,4,5-tetra-methylsulfonamide).

The incorporation of transition metal centers not only enables intrinsic high electrical conductivity, but also shows an impressive redox potential increase of as high as 1 V as compared to A₄-PTtSA analogues, resulting in a class of organometallic cathode materials with a high average redox potential of 2.95–3.25 V for Li-, Na- and K-ion batteries.

—Wang et al.

The researchers said that these results provide guidelines for higher capacity materials by designing systems with also reversible redox of transition metals, while also provide opportunities for exploring divalent or trivalent cations in this class of conducting coordination polymers.

Resources

• Jiande Wang, Xiaolong Guo, Petru Apostol, Xuelian Liu, Koen Robeyns, Loïk Gence, Cristian Morari, Jean-François Gohy and Alexandru Vlad (2022) “High performance Li-, Na-, and K-ion storage in electrically conducting coordination polymers” Energy Environ. Sci., doi: 10.1039/D2EE00566B