A High‐Energy and Safe Lithium Battery Enabled by Solid‐State Redox Chemistry in a Fireproof Gel Electrolyte

Abstract

eliminate the trouble of such aggressive cell chemistry. [2][3][4][5][6] Applying the oxide cathodes (e.g., LiCoO 2 , LiNi x Mn 1-x O 4 ) in commercial cell design further risks the cell by severe exothermic side reactions of released oxygen radicals with flammable liquid electrolytes. [7,8] Developing less reactive but energetic redox chemistry offers a more realistic option to fulfill the demand of high energy and reliability. Lithium sulfide (Li 2 S) is particularly attractive to this goal due to superior Li content (66.67 at%) and capacity (1166 mA h g -1 ) to the common cathodes as well as stable redox free of reactive Li metal and oxygen species. It also far excels high-capacity sulfur cathode in thermal stability and compatibility with lithium-free high-capacity anodes (e.g., Si, Sn, and metal oxides). When coupled with Si anode, high theoretical energy of 1550 W h kg -1 can be achieved beyond the existing LIBs. [9] More attractive, the hazards of reactive Li metal and oxygen-releasing electrodes can be fully eliminated to secure high safety with less sacrifice of cell energy. These benefits make the Li 2 S-based lithium batteries highly promising in powerful yet reliable energy storage.Practical use of Li 2 S cathode is primarily hindered by the huge activation barrier and sluggish charge kinetics that stems from the insulating character and robust ionic lattice of Li 2 S. [10] Applying conductive matrix, redox mediators and/or electrocatalysis can lower but hardly minimize these difficulties even in nanostructured design. [11][12][13] Usually, the Li 2 S cathodes undergo a solid-liquid-solid redox pathway in the ether-based electrolytes to release soluble lithium polysulfides (LiPS) as indispensable redox mediators. Under concentration gradient and electrical force, these species diffuse into the electrolyte, inducing irreversible capacity loss and anode passivation to damage cell reversibility. [14] These problems can be mitigated to some extent by physical trapping and/or chemical anchoring of LiPS plus adding LiPS-repelling interlayer or LiNO 3 additive to stabilize the electrode interface. [15][16][17][18][19][20] Gel electrolytes with limited LiPS solubility and mobility also work effectively in restricting the LiPS loss. [21] Nevertheless, these approaches are hard to fully address the LiPS since the LiPS is indispensable for relaying solid-liquid-solid redox of Li 2 S cathode. Transforming the redox conversion of Li 2 S to the direct solid-solid process without LiPS is the ultimate solution to this difficulty. But the absence of LiPS as the redox mediators makes electrochemical oxidation Recent years have witnessed thriving efforts in pursuing high-energy batteries at an unaffordable cost of safety. Herein, a high-energy and safe quasi-solid-state lithium battery is proposed by solid-state redox chemistry of polymer-based molecular Li 2 S cathode in a fireproof gel electrolyte. This chemistry fully eliminates not only the negative effect of extremely reactive Li metal and oxygen species on cell sa...

A Solid-State Lithium Battery with PVDF–HFP-Modified Fireproof Ionogel Polymer Electrolyte

“…Meanwhile, commercial PP diaphragms and CIME films were subjected to combustion tests (Figure S4); MXene is oxidized and forms a protective TiO 2 /C layer on the surface of the polymer substrate at high temperatures and in air but does not destroy the original laminate structure. The protective layer allows heat exchange and reduces the combustion rate of the composite, while the barrier effect of the lamellar structure effectively prevents combustion and the introduction of ionic liquids made the CIME less combustible. , Thermodynamic and kinetic changes of electrolytes were studied by differential scanning calorimetry (DSC) in Figure c; it is possible to know that the melting temperature ( T m ) of pure PVDF–HFP film is 141.7 °C. However, the addition of EmimTFSI affected the crystallinity of PVDF–HFP, resulting in a decrease in T m value to 107.8 °C.…”

Diagnosing and Correcting the Failure of the Solid‐State Polymer Electrolyte for Enhancing Solid‐State Lithium–Sulfur Batteries

“…Phase transition of Li 2 S@SA-Ni@HCS cathode in SPE is monitored by in operando XRD analysis of working cells for understanding the effect of SA-Ni catalyst on propelling the kinetics of Li-S redox conversion. [45,46] The initial charge of this cathode involves three primary steps: i) Li 2 S activation at a rather low potential barrier of 2.4 V; ii) complete Li 2 S dis-sociation to LiPS at 2.39 V until 56% depth of charge; iii) rapid LiPS conversion to sulfur since 66% depth of charge (Figure 4a). In sharp contrast, the SA-Ni free Li 2 S@HCS cathode encounters sluggish kinetics, as reflected by slow yet incomplete Li 2 S dissociation with much higher activation potential (2.88 V) even charged to 3.5 V. In the presence of SA-Ni catalyst, the rate of Li 2 S dissociation could be doubled at least upon charge (Figure S15, Supporting Information).…”

Working Principles of Lithium Metal Anode in Pouch Cells

“…The "marriage" of SSE and Li metal anode is considered the essential route for realizing the nextgeneration high-energy-density LMBs. [203,204] Compared with conventional liquid electrolytes, the reactivity of SSEs with Li metal is greatly reduced, [205] and the high mechanical modulus of SSEs also inhibits the growth of Li dendrites. Therefore, SSE offers the possibility for the safe and efficient operation of Li metal anodes.…”