Lithium Ion Repulsion-Enrichment Synergism Induced by Core-Shell Ionic Complexes to Enable High-Loading Lithium Metal Batteries.

A core-shell additive with anionic Keggin-type polyoxometalate (POM) cluster as core and N-containing cation of ionic liquid (IL) as shell is proposed to stabilize Li-metal batteries (LMBs). The suspended POM derived complex in ether-based electrolyte is absorbed around the protuberances of anode and triggers a lithiophobic repulsion mechanism for the homogenization of Li+ redistribution. The gradually released POM cores with negative charge then enrich Li+ and co-assemble with Li. The Li+ repulsion-enrichment synergism can compact Li deposition and reinforce solid electrolyte interphase. This sustained-release additive enables Li∥Li symmetric cells with a long lifetime over 500 h and 300 h at high current densities of 3 and 5 mA cm-2 respectively. The complex additive is also compatible with high-voltage Li∥LiNi0.8 Co0.15 Al0.05 O2 (NCA) cells. Even with a NCA loading as high as ca. 20 mg cm-2 , the additive contained Li∥NCA cell can still cycle for over 100 cycles at 2.6 mA cm-2 .

Dual strategies of mild C-F scissoring fluorination and local high-concentration electrolyte to enable reversible Li-Fe-F conversion batteries.

Batteries taking conversion-type iron fluorides as energy-dense cathodes provide the possibility for the power electrification of the transportation and aviation industries. However, a safe and low-toxicity synthesis method for fluorides and the design of a compatible electrolyte formula are still challenging. Here, we propose a dual strategy of mild C-F scissoring fluorination and a local high-concentration electrolyte (LHCE) to enable highly reversible Li-Fe-F conversion batteries. A facile and safe scissoring strategy at a low temperature (95 °C) enables the preparation of a carbon-iron fluoride composite with a porous cubic cage-like structure. CFx plays a double role as a solid fluorination agent and an in situ conductive network after defluorination. The as-prepared fluoride cathode delivers a reversible capacity as high as 300 mA h g-1 over 100 cycles. The further LHCE strategy not only enhances the oxidation stable voltage of the electrolyte (>5 V) and the transference number of Li+ (0.74), but also realizes dual protection of the fluoride cathode and Li metal anode by facilitating the construction of robust cathode- and anode-electrolyte interfaces, respectively. The LHCE-assisted fluoride battery releases a higher reversible capacity of 335 mA h g-1 after 130 cycles. This work provides a solution to high-performance carbon-fluoride conversion cathodes by a synergetic effect of tailored synthesis, electroactive particle texture and electrolyte formula.

Dual fluorination of polymer electrolyte and conversion-type cathode for high-capacity all-solid-state lithium metal batteries.

All-solid-state batteries are appealing electrochemical energy storage devices because of their high energy content and safety. However, their practical development is hindered by inadequate cycling performances due to poor reaction reversibility, electrolyte thickening and electrode passivation. Here, to circumvent these issues, we propose a fluorination strategy for the positive electrode and solid polymeric electrolyte. We develop thin laminated all-solid-state Li||FeF3 lab-scale cells capable of delivering an initial specific discharge capacity of about 600 mAh/g at 700 mA/g and a final capacity of about 200 mAh/g after 900 cycles at 60 °C. We demonstrate that the polymer electrolyte containing AlF3 particles enables a Li-ion transference number of 0.67 at 60 °C. The fluorinated polymeric solid electrolyte favours the formation of ionically conductive components in the Li metal electrode's solid electrolyte interphase, also hindering dendritic growth. Furthermore, the F-rich solid electrolyte facilitates the Li-ion storage reversibility of the FeF3-based positive electrode and decreases the interfacial resistances and polarizations at both electrodes.

Construction of solid-liquid fluorine transport channel to enable highly reversible conversion cathodes.

Conversion-type iron fluoride is a promising alternative cathode to intercalation oxides because of its higher energy density. However, its intrinsic solid-solid conversion is sluggish during repeated splitting and rebonding of metal-fluorine moieties. Here, we propose a solid-liquid conversion mechanism to activate the fluorine transport kinetics of iron oxyfluorides enabled by fluoride anion receptor of tris(pentafluorophenyl)borane (TPFPB). TPFPB promotes the dissociation of inert lithium fluoride and provides a facile fluorine transport channel at multiphase interfaces via the formation of solvated F− intermediate therein. The construction of solid-liquid channel with fluorinated cathode electrolyte interface is the key for the achievement of FeO0.3F1.7 and FeO0.7F1.3 in terms of sustaining conversion reaction (with an energy efficiency approaching 80%) and high-rate performance (with reversible capacity of 320 mAh/g at 2 A/g). The cathode energy densities can reach 1100 Wh/kg for FeO0.3F1.7 and 700 Wh/kg for FeO0.7F1.3 under the power densities of 220 and 4300 W/kg, respectively.