No abstract

Multivalent‐ion batteries are emerging as low‐cost, high energy density, and safe alternatives to Li‐ion batteries but are challenged by slow cation diffusion in electrode materials due to the high polarization strength of Mg‐ and Al‐ions. In contrast, Ca‐ion has a low polarization strength similar to that of Li‐ion, therefore a Ca‐ion battery will share the advantages while avoiding the kinetics issues related to multivalent batteries. However, there is no battery known that utilizes the Ca‐ion chemistry due to the limited success in Ca‐ion storage materials. Here, a safe and low‐cost aqueous Ca‐ion battery based on a highly reversible polyimide anode and a high‐potential open framework copper hexacyanoferrate cathode is demonstrated. The prototype cell shows a stable capacity and high efficiency at both high and low current rates, with an 88% capacity retention and an average 99% coloumbic efficiency after cycling at 10C for 1000 cycles. The Ca‐ion storage mechanism for both electrodes as well as the origin of the fast kinetics have been investigated. Additional comparison with a Mg‐ion cell with identical electrodes reveals clear kinetics advantages for the Ca‐ion system, which is explained by the smaller ionic radii and more facile desolvation of hydrated Ca‐ions.

Magnesium batteries have long been pursued as potentially high-energy and safe alternatives to Li-ion batteries; however, fast chargedischarge capability, one of the most desired properties for advanced batteries, remains elusive for this technology. Here, we develop a next generation Mg battery prototype, delivering a specific energy of up to 566 Wh kg 1 and an ultrahigh specific power of up to 30.4 kW kg 1 , which is close to two orders of magnitude higher than state-of-the-art Mg battery. This is achieved by coupling a kinetically fast organic cathode material, operating under bond cleavage-free solidliquid reaction, and an electrolyte capable of providing dendrite-free Mg depositionstripping at a record current density of 20 mA cm 2 .One Sentence Summary: Ultrahigh power, an unprecedented quality of Mg battery, is unveiled and demonstrated using a prototype combining a quinone-based cathode and a second to none Mg(CB 11 H 12 ) 2 electrolyte that enables ultrahigh rate cycling of dendrite-free Mg anode.

In typical chloride-containing electrolytes, storage of MgCl + is dominant in organic cathodes. The negative impact of the MgCl-storage chemistry on the specific energy was elucidated through cell tests with controlled amounts of electrolyte. With the right combination of organic cathodes and chloride-free electrolytes, storage of Mg 2+ in organic electrodes can be realized. The Mg-storage chemistry has also enabled the first Mg battery that operates under lean electrolyte conditions, which has important implications for the practicality of high-energy organic Mg batteries.

Magnesium rechargeable batteries potentially offer high-energy density, safety, and low cost due to the ability to employ divalent, dendrite-free, and earth-abundant magnesium metal anode. Despite recent progress, further development remains stagnated mainly due to the sluggish scission of magnesium-chloride bond and slow diffusion of divalent magnesium cations in cathodes. Here we report a battery chemistry that utilizes magnesium monochloride cations in expanded titanium disulfide. Combined theoretical modeling, spectroscopic analysis, and electrochemical study reveal fast diffusion kinetics of magnesium monochloride cations without scission of magnesium-chloride bond. The battery demonstrates the reversible intercalation of 1 and 1.7 magnesium monochloride cations per titanium at 25 and 60 °C, respectively, corresponding to up to 400 mAh g−1 capacity based on the mass of titanium disulfide. The large capacity accompanies with excellent rate and cycling performances even at room temperature, opening up possibilities for a variety of effective intercalation hosts for multivalent-ion batteries.