No abstract

In carbonate electrolytes, the organic–inorganic solid electrolyte interphase (SEI) formed on the Li‐metal anode surface is strongly bonded to Li and experiences the same volume change as Li, thus it undergoes continuous cracking/reformation during plating/stripping cycles. Here, an inorganic‐rich SEI is designed on a Li‐metal surface to reduce its bonding energy with Li metal by dissolving 4m concentrated LiNO3 in dimethyl sulfoxide (DMSO) as an additive for a fluoroethylene‐carbonate (FEC)‐based electrolyte. Due to the aggregate structure of NO3− ions and their participation in the primary Li+ solvation sheath, abundant Li2O, Li3N, and LiNxOy grains are formed in the resulting SEI, in addition to the uniform LiF distribution from the reduction of PF6− ions. The weak bonding of the SEI (high interface energy) to Li can effectively promote Li diffusion along the SEI/Li interface and prevent Li dendrite penetration into the SEI. As a result, our designed carbonate electrolyte enables a Li anode to achieve a high Li plating/stripping Coulombic efficiency of 99.55 % (1 mA cm−2, 1.0 mAh cm−2) and the electrolyte also enables a Li||LiNi0.8Co0.1Mn0.1O2 (NMC811) full cell (2.5 mAh cm−2) to retain 75 % of its initial capacity after 200 cycles with an outstanding CE of 99.83 %.

Development of electrolytes that simultaneously have high ionic conductivity, wide electrochemical window, and lithium dendrite suppression ability is urgently required for high‐energy lithium‐metal batteries (LMBs). Herein, an electrolyte is designed by adding a countersolvent into LiFSI/DMC (lithium bis(fluorosulfonyl)amide/dimethyl carbonate) electrolytes, forming countersolvent electrolytes, in which the countersolvent is immiscible with the salt but miscible with the carbonate solvents. The solvation structure and unique properties of the countersolvent electrolyte are investigated by combining electroanalytical technology with a Molecular Dynamics simulation. Introducing the countersolvent alters the coordination shell of Li+ cations and enhances the interaction between Li+ cations and FSI− anions, which leads to the formation of a LiF‐rich solid electrolyte interphase, arising from the preferential reduction of FSI− anions. Notably, the countersolvent electrolyte suppresses Li dendrites and enables stable cycling performance of a Li||NCM622 battery at a high cut‐off voltage of 4.6 V at both 25 and 60 °C. This study provides an avenue to understand and design electrolytes for high‐energy LMBs in the future.

More importantly, the high mechanical strength is expected to block the lithium dendrite penetration. [5] The unit transference number of Li-ions in SSEs should prevent concentration gradient-induced Li dendrite growth in SSEs. [6] However, extensive investigations demonstrated that Li dendrites still easily grow in inorganic SSEs, including Li 3 PS 4 (LPS), [7] and Li 7 La 3 Zr 2 O 12 (LLZO), [8] whatever they are in single crystal, [9] amorphous or multicrystal structures. The SSEs with much higher mechanical strength show even lower dendrite suppression capability than that in conventional organic electrolytes. [10] Both intergranularly [11] and intragranularly Li dendrite growth are found in SSEs. [12] However, the mechanism for Li dendrite growth in SSEs is not fully understood. Hypotheses, such as poor interfacial contact, electronic conductivity of bulk electrolytes, and the presence of the grain boundaries (GBs), are proposed to illustrate the counterintuitive dendrite growth in SSEs. [13] The high interfacial resistance and non-uniformity at Li/SSE interface, introducing by GBs, voids, and cracks, are often blamed to be responsible for the Li dendrite growth in SSEs. [13] However, reduction of the non-uniformity by densifying SSE, [14] amorphous SSE, and single crystal SSE [15] cannot block the Li dendrite growth. In addition, to reduce the interfacial resistance, lithiophilic Au, [16] Al 2 O 3 , [17] ZnO, [18] Ge, [19] and Li 3 N, [20] which bridges the energy gap between Li and SSE, were coated on SSEs and lithiophobic Li 2 CO 3 was removed from LLZO surface by polishing and heating. [21] However, Li dendrites still grow in SSEs even though the interface resistance is reduced. [22,23] In sharp contrast to lithiophilic coating and enhancement of the uniformity of SSEs, herein, we design a lithiophobic porous SSE that has a high interface energy against Li, a high ionic conductivity and low electronic conductivity to enhance the dendrite suppression capability. Based on the total energy analyses, we established dendrite suppression criterion: the electrolytes or formed interphases should: 1) be electrochemically stable with Li; 2) have a high ionic conductivity and a low electronic conductivity; and 3) have a high interface energy against Li to suppress Li nucleation and growth inside electrolytes. Li 3 N has a high ion conductivity and is stable with Li metal. However, All-solid-state Li metal batteries have attracted extensive attention due to their high safety and high energy density. However, Li dendrite growth in solid-state electrolytes (SSEs) still hinders their application. Current efforts mainly aim to reduce the interfacial resistance, neglecting the intrinsic dendrite-suppression capability of SSEs. Herein, the mechanism for the formation of Li dendrites is investigated, and Li-dendrite-free SSE criteria are reported. To achieve a high dendrite-suppression capability, SSEs should be thermodynamically stable with a high interface energy against Li, and they should have a low electronic conducti...

The lithium metal anode is considered as the ultimate choice for high-energy-density batteries. However, the organic-dominated solid electrolyte interphase (SEI) formed in carbonate electrolytes has a low interface energy against metallic Li as well as a high resistance, resulting in a low Li plating/stripping Coulombic efficiency (CE) of less than 99.0% and severe Li dendrite growth. Herein, inorganic-enhanced LiF-Li3N SEI is designed in commercial 1 M LiPF6/EC-DMC electrolytes by introducing lithium nitrate (LiNO3) and fluoroethylene carbonate (FEC) through a small amount of sulfolane (SL) as a carrier solvent owing to the high solubility of SL for both carbonate solvents and LiNO3. The comprehensive characterizations and simulations demonstrate that the synergistic interaction of LiNO3 and FEC additives alters the solvation structure of 1 M LiPF6/EC-DMC electrolytes and forms additive-derived LiF-Li3N SEI, which increases the average Li CE up to 99.6% in 100 cycles. The designed carbonate electrolyte enables the Li/LiNi0.80Co0.15Al0.05O2 (NCA) cell with a lean lithium metal anode (∼50 μm) to achieve an average CE of 99.7% and a high capacity retention of 90.8% after 150 cycles. This work offers a simple and economical strategy to realize high-performance lithium metal batteries in commercial carbonate electrolytes.

No abstract

Water‐in‐salt electrolytes (WISE) have largely widened the electrochemical stability window (ESW) of aqueous electrolytes by formation of passivating solid electrolyte interphase (SEI) on anode and also absorption of the hydrophobic anion‐rich double layer on cathode. However, the cathodic limiting potential of WISE is still too high for most high‐capacity anodes in aqueous sodium‐ion batteries (ASIBs), and the cost of WISE is also too high for practical application. Herein, a low‐cost 19 m (m: mol kg−1) bi‐salts WISE with a wide ESW of 2.8 V was designed, where the low‐cost 17 m NaClO4 extends the anodic limiting potential to 4.4 V, while the fluorine‐containing salt (2 m NaOTF) extends the cathodic limiting potential to 1.6 V by forming the NaF–Na2O–NaOH SEI on anode. The 19 m NaClO4–NaOTF–H2O electrolyte enables a 1.75 V Na3V2(PO4)3∥Na3V2(PO4)3 full cell to deliver an appreciable energy density of 70 Wh kg−1 at 1 C with a capacity retention of 87.5 % after 100 cycles.

LiNi x Co y Mn z O 2 (x + y + z = 1) j j graphite lithium-ion battery (LIB) chemistry promises practical applications. However, its low-temperature (� À 20 °C) performance is poor because the increased resistance encountered by Li + transport in and across the bulk electrolytes and the electrolyte/electrode interphases induces capacity loss and battery failures. Though tremendous efforts have been made, there is still no effective way to reduce the charge transfer resistance (R ct ) which dominates low-temperature LIBs performance. Herein, we propose a strategy of using lowpolarity-solvent electrolytes which have weak interactions between the solvents and the Li + to reduce R ct , achieving facile Li + transport at sub-zero temperatures. The exemplary electrolyte enables LiNi 0.8 Mn 0.1 Co 0.1 O 2 j j graphite cells to deliver a capacity of � 113 mAh g À 1 (98 % full-cell capacity) at 25 °C and to remain 82 % of their room-temperature capacity at À 20 °C without lithium plating at 1/3C. They also retain 84 % of their capacity at À 30 °C and 78 % of their capacity at À 40 °C and show stable cycling at 50 °C.