No abstract

hydrogen electrode), lithium metal is regarded as a promising anode candidate for next-generation high-performance lithium batteries (LMBs) technology. [1][2][3] However, the highly reactive Li metal anode, being incompatible with the stateof-the-art carbonate-based electrolytes, induces unwanted electrolyte decompositions and unstable solid electrolyte interface (SEI) during electrochemical cycling. It is also noted that the repeated Li stripping and plating results in uncontrollable Li dendrites growth as well as rapid anode pulverization. [4][5][6][7] Although the ether-based electrolytes possess relatively better (electro)chemical compatibility with Li metal, yet their low oxidation stability makes them challenging for high-voltage LMBs. [2,[8][9][10][11][12] Notably, most of carbonate and ether electrolytes are volatile and flammable, posing severe safety threats to the implementation of LMBs. In order to tackle these challenges, several promising electrolyte-design proposals, such as adopting solid-state electrolytes, developing flame-retardant electrolytes, and engineering ionic liquid electrolytes, have been widely explored. [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] These strategies have mitigated these challenges to some extent, yet they, unfortunately, lead to higher viscosities and/or lower ionic conductivities, undermining the overall electrochemical performance of LMBs. [29] Hence, formulating an advanced electrolyte that possesses simultaneously a wide electrochemical window, a high ionic conductivity, and improved safety characteristic is highly desirable for advancing the development of high-voltage and highsafety LMBs.Succinonitrile (SN)-based electrolyte is one of the most promising electrolytes for high-performance LMBs owing to its high oxidative stability and fast ionic conduction capability. [30] Wen's group has designed and fabricated several SN-based electrolytes for LMBs. [31][32][33][34] These SN-based electrolytes are successfully used as solid-state electrolytes. The reason why SN was rarely employed as the major component of a liquid electrolyte is its insufficient reductive compatibility in contact with Li anode. [35,36] Previous reports demonstrate that the Lewis bases (e.g., Li metal) could easily extract the SN α-hydrogen Severe safety concerns and uncontrollable lithium dendrites are major challenges for commercializing high-voltage lithium metal batteries (LMBs) utilizing state-of-the-art carbonate-based electrolytes. Herein, a new type of deep eutectic electrolyte (succinonitrile/1,3,5-trioxane/lithium difluoro(oxalato) borate (DFOB), abbreviated as DEE) with a thermally induced smart shutdown function is presented to ameliorate the aforementioned issues. In this delicately designed DEE, 1,3,5-trioxane (TXE) can participate in the Li + primary solvation shell and form an unique solvation structure (Li + -SN-TXE-DFOB − ), which is favorable to enhance the Li/electrolyte interfacial compatibility. It is demonstrated that a 4.45 V LiCoO 2 /Li battery using t...

The recent concept of "molecular crowding agents" offering hydrogen bond (H-bond) accepting sites for free water molecules has alleviated parasitic hydrogen evolution in aqueous electrolytes. However, their cathodic limits are still not low enough to be compatible with the energy-dense Li 4 Ti 5 O 12 anode (1.55 V vs Li + /Li). Inspired by nature's choice of a peptide unit featuring an amide group in forming extensive H-bond networks with water, herein, we select caprolactam, an imide analogous to the amide group in a peptide, to reduce water activity via regulating the H-bond. The introduced caprolactam containing both an H-bond acceptor and donor effectively confines water molecules in a double-site anchoring configuration with strengthened H-bonding interactions and interrupts the original H-bonding among water molecules. This unique solution structure delays the onset potential of hydrogen evolution to 1.3 V vs Li + /Li, which enables the cycling of a Li 4 Ti 5 O 12 /LiMn 2 O 4 full cell with an average Coulombic efficiency of 99.7% and 78% capacity retention after 350 cycles.

Lithium batteries have been widely used in various fields such as portable electronic devices, electric vehicles, and grid storages devices. However, the low temperature‐tolerant performances (−70 to 0 °C) of lithium batteries are still mainly hampered by low ionic conductivity of bulk electrolyte and interfacial issues. In general, there are four threats in developing low‐temperature lithium batteries when using traditional carbonate‐based electrolytes: 1) low ionic conductivity of bulk electrolyte, 2) increased resistance of solid electrolyte interphase (SEI), 3) sluggish kinetics of charge transfer, 4) slow Li diffusion throughout bulk electrodes. Meanwhile, conventional electrolytes have been close to the upper limit of optimum low‐temperature performance owing to their intrinsic molecular structural properties. As a result, it is urgent to design unconventional electrolytes with lower melting point and higher ionic conductivity. Herein, the recent key advances in regard to unconventional electrolytes including fluorinated ester, ethyl acetate, gamma‐butyrolactone, liquefied gas, ether, plastic crystal, and aqueous electrolytes are overviewed. Solvation structure modification and SEI optimization of unconventional electrolytes for low‐temperature lithium batteries are focused. Finally, aiming at the deficiencies in current understanding, the inherent limitations and envision the future prospects of low‐temperature lithium batteries are explored.

Solid-state polymer electrolytes are an important factor in the deployment of highsafety and high-energy-density solid-state lithium metal batteries. Nevertheless, use of the traditional polyethylene oxide-based solid-state polymer electrolyte is limited due to its inherently low ionic conductivity and narrow electrochemical stability window. Herein, for the first time, we specifically designed a cyanoethyl cellulosein-deep eutectic solvent composite eutectogel as a promising candidate for hybrid solid-state polymer electrolytes. It is found that the proposed eutectogel electrolyte achieves high ionic conductivity (1.87 × 10 −3 S cm −1 at 25°C), superior electrochemical stability (up to 4.8 V), and outstanding lithium plating/striping behavior (low overpotential of 0.04 V at 1 mA cm −2 and 1 mA h cm −2 over 300 h). With the eutectogel-based solid-state polymer electrolyte, a 4.45 V LiCoO 2 /Li metal battery delivers prominent long-term lifespan (capacity retention of 85% after 200 cycles) and high average Coulombic efficiency (99.5%) under ambient conditions, significantly outperforming the traditional carbonate-based liquid electrolyte. Our work demonstrates a promising strategy for designing eutectogel-based solid-state polymer electrolytes to realize high-voltage and high-energy lithium metal batteries.