Fast Interfacial Defluorination Kinetics Enables Stable Cycling of Low-Temperature Lithium Metal Batteries.

The development of low-temperature lithium metal batteries (LMBs) encounters significant challenges because of severe dendritic lithium growth during the charging/discharging processes. To date, the precise origin of lithium dendrite formation still remains elusive due to the intricate interplay between the highly reactive lithium metal anode and organic electrolytes. Herein, we unveil the critical role of interfacial defluorination kinetics of localized high-concentration electrolytes (LHCEs) in regulating lithium dendrite formation, thereby determining the performance of low-temperature LMBs. We investigate the impact of solvation structures of LHCEs on low-temperature LMBs by employing tetrahydrofuran (THF) and 2-methyltetrahydrofuran (2-MeTHF) as comparative solvents. The combination of comprehensive characterizations and theoretical simulations reveals that the THF-based LHCE featured with a strong solvation strength exhibits fast interfacial defluorination reaction kinetics, thus leading to the formation of an amorphous and inorganic-rich solid-electrolyte interphase (SEI) that can effectively suppress the growth of lithium dendrites. As a result, the highly reversible Li metal anode achieves an exceptional Coulombic efficiency (CE) of up to ∼99.63% at a low temperature of -30 °C, thereby enabling stable cycling of low-temperature LMB full cells. These findings underscore the crucial role of electrolyte interfacial reaction kinetics in shaping SEI formation and provide valuable insights into the fundamental understanding of electrolyte chemistry in LMBs.

Amorphous Chloride Solid Electrolytes with High Li-Ion Conductivity for Stable Cycling of All-Solid-State High-Nickel Cathodes.

Solid electrolytes (SEs) are central components that enable high-performance, all-solid-state lithium batteries (ASSLBs). Amorphous SEs hold great potential for ASSLBs because their grain-boundary-free characteristics facilitate intact solid-solid contact and uniform Li-ion conduction for high-performance cathodes. However, amorphous oxide SEs with limited ionic conductivities and glassy sulfide SEs with narrow electrochemical windows cannot sustain high-nickel cathodes. Herein, we report a class of amorphous Li-Ta-Cl-based chloride SEs possessing high Li-ion conductivity (up to 7.16 mS cm-1) and low Young's modulus (approximately 3 GPa) to enable excellent Li-ion conduction and intact physical contact among rigid components in ASSLBs. We reveal that the amorphous Li-Ta-Cl matrix is composed of LiCl43-, LiCl54-, LiCl65- polyhedra, and TaCl6- octahedra via machine-learning simulation, solid-state 7Li nuclear magnetic resonance, and X-ray absorption analysis. Attractively, our amorphous chloride SEs exhibit excellent compatibility with high-nickel cathodes. We demonstrate that ASSLBs comprising amorphous chloride SEs and high-nickel single-crystal cathodes (LiNi0.88Co0.07Mn0.05O2) exhibit ∼99% capacity retention after 800 cycles at ∼3 C under 1 mA h cm-2 and ∼80% capacity retention after 75 cycles at 0.2 C under a high areal capacity of 5 mA h cm-2. Most importantly, a stable operation of up to 9800 cycles with a capacity retention of ∼77% at a high rate of 3.4 C can be achieved in a freezing environment of -10 °C. Our amorphous chloride SEs will pave the way to realize high-performance high-nickel cathodes for high-energy-density ASSLBs.

Origin of dendrite-free lithium deposition in concentrated electrolytes.

The electrolyte solvation structure and the solid-electrolyte interphase (SEI) formation are critical to dictate the morphology of lithium deposition in organic electrolytes. However, the link between the electrolyte solvation structure and SEI composition and its implications on lithium morphology evolution are poorly understood. Herein, we use a single-salt and single-solvent model electrolyte system to systematically study the correlation between the electrolyte solvation structure, SEI formation process and lithium deposition morphology. The mechanism of lithium deposition is thoroughly investigated using cryo-electron microscopy characterizations and computational simulations. It is observed that, in the high concentration electrolytes, concentrated Li+ and anion-dominated solvation structure initiate the uniform Li nucleation kinetically and favor the decomposition of anions rather than solvents, resulting in inorganic-rich amorphous SEI with high interface energy, which thermodynamically facilitates the formation of granular Li. On the contrary, solvent-dominated solvation structure in the low concentration electrolytes tends to exacerbate the solvolysis process, forming organic-rich mosaic SEI with low interface energy, which leads to aggregated whisker-like nucleation and growth. These results are helpful to tackle the long-standing question on the origin of lithium dendrite formation and guide the rational design of high-performance electrolytes for advanced lithium metal batteries.

Constructing Three-Dimensional Topological Zn Deposition for Long-Life Aqueous Zn-Ion Batteries.

Uniform and compact Zn deposition-dissolution is essential to achieve high Coulombic efficiency and long lifespan for Zn anodes. More attention has been commonly focused on the suppression of macroscopic Zn dendrites in the previous reports. The rational control of the microstructure of Zn deposition to prevent the intrinsic volume expansion and pulverization of Zn metal so as to stabilize Zn anodes is less discussed. Herein, we construct a three-dimensional topological Zn deposition at the nanoscale through an in situ electrochemical process in the optimal hybrid aqueous electrolyte. The topological electrode structure can efficiently accommodate microscopic strain and volume variation and thus largely preserve the macroscopic integrity and electrical contact of Zn anodes, leading to enhanced reversibility and stability. With the unique topological structure of Zn deposition, the Coulombic efficiency of Zn anodes could reach >99.9% with excellent cycling over 1182 h at 2 mA cm-2 and 2 mA h cm-2 (Zn utilization: 11.4%). The evolution of "dead" Zn during repeated cycling is first investigated using a homemade semiquantitative analysis method to determine the critical "short slab" for aqueous Zn batteries under the practical application. This work provides an insightful method to regulate the microscopic morphology of Zn deposition for high-performance Zn batteries.

Rational Design of an Artificial SEI: Alloy/Solid Electrolyte Hybrid Layer for a Highly Reversible Na and K Metal Anode.

The practical application of a Na/K-metallic anode is intrinsically hindered by the poor cycle life and safety issues due to the unstable electrode/electrolyte interface and uncontrolled dendrite growth during cycling. Herein, we solve these issues through an in situ reaction of an oxyhalogenide (BiOCl) and Na to construct an artificial solid electrolyte interphase (SEI) layer consisting of an alloy (Na3Bi) and a solid electrolyte (Na3OCl) on the surface of the Na anode. As demonstrated by theoretical and experimental results, such an artificial SEI layer combines the synergistic properties of high ionic conductivity, electronic insulation, and interfacial stability, leading to uniform dendrite-free Na deposition beneath the hybrid SEI layer. The protected Na anode presents a low voltage polarization of 30 mV, achieving an extended cycling life of 700 h at 1 mA cm-2 in the carbonate-based electrolyte. The full cell based on the Na3V2(PO4)3 cathode and hybrid SEI-protected Na anode shows long-term stability. When this strategy is applied to a K metal anode, the protected K anode also reaches a cycling life of over 4000 h at 0.5 mA cm-2 with a low voltage polarization of 100 mV. Our work provides an important insight into the design principles of a stable artificial SEI layer for high-energy-density metal batteries.

Revisiting the Role of Physical Confinement and Chemical Regulation of 3D Hosts for Dendrite-Free Li Metal Anode.

Lithium metal anode has been demonstrated as the most promising anode for lithium batteries because of its high theoretical capacity, but infinite volume change and dendritic growth during Li electrodeposition have prevented its practical applications. Both physical morphology confinement and chemical adsorption/diffusion regulation are two crucial approaches to designing lithiophilic materials to alleviate dendrite of Li metal anode. However, their roles in suppressing dendrite growth for long-life Li anode are not fully understood yet. Herein, three different Ni-based nanosheet arrays (NiO-NS, Ni3N-NS, and Ni5P4-NS) on carbon cloth as proof-of-concept lithiophilic frameworks are proposed for Li metal anodes. The two-dimensional nanoarray is more promising to facilitate uniform Li+ flow and electric field. Compared with the NiO-NS and the Ni5P4-NS, the Ni3N-NS on carbon cloth after reacting with molten Li (Li-Ni/Li3N-NS@CC) can afford the strongest adsorption to Li+ and the most rapid Li+ diffusion path. Therefore, the Li-Ni/Li3N-NS@CC electrode realizes the lowest overpotential and the most excellent electrochemical performance (60 mA cm-2 and 60 mAh cm-2 for 1000 h). Furthermore, a remarkable full battery (LiFePO4||Li-Ni/Li3N-NS@CC) reaches 300 cycles at 2C. This research provides valuable insight into designing dendrite-free alkali metal batteries.

Surface Transformation Enables a Dendrite-Free Zinc-Metal Anode in Nonaqueous Electrolyte.

Significant challenges remain in developing rechargeable zinc batteries mainly because of reversibility problems on zinc-metal anodes. The dendritic growth and hydrogen evolution on zinc electrodes are major obstacles to overcome in developing practical and safe zinc batteries. Here, a dendrite-free and hydrogen-free Zn-metal anode with high Coulombic efficiency up to 99.6% over 300 cycles is realized in a newly designed nonaqueous electrolyte, which comprises an inexpensive zinc salt, zinc acetate, and a green low-cost solvent, dimethyl sulfoxide. Surface transformation on Cu substrate plays a critical role in facilitating the dendrite-free deposition process, which lowers the diffusion energy barrier of the Zn atoms, leading to a uniform and compact thin film for zinc plating. Furthermore, in situ electrochemical atomic force microscopy reveals the plating process via a layer-by-layer growth mechanism and the stripping process through an edge-dissolution mechanism. In addition, Zn||Mo6 S8 full cells exhibit excellent electrochemical performance in terms of cycling stability and rate capability. This work presents a new opportunity to develop nonaqueous rechargeable zinc batteries.

Artificial Heterogeneous Interphase Layer with Boosted Ion Affinity and Diffusion for Na/K-Metal Batteries.

Metallic Na (K) are considered a promising anode materials for Na-metal and K-metal batteries because of their high theoretical capacity, low electrode potential, and abundant resources. However, the uncontrolled growth of Na (K) dendrites severely damages the stability of the electrode/electrolyte interface, resulting in battery failure. Herein, a heterogeneous interface layer consisting of metal vanadium nanoparticles and sodium sulfide (potassium sulfide) is introduced on the surface of a Na (K) foil (i.e., Na2 S/V/Na or K2 S/V/K). Experimental studies and theoretical calculations indicate that a heterogeneous Na2 S/V (K2 S/V) protective layer can effectively improve Na (K)-ion adsorption and diffusion kinetics, inhibiting the growth of Na (K) dendrites during Na (K) plating/stripping. Based on the novel design of the heterogeneous layer, the symmetric Na2 S/V/Na cell displays a long lifespan of over 1000 h in a carbonate-based electrolyte, and the K2 S/V/K electrode can operate for over 1300 h at 0.5 mA cm-2 with a capacity of 0.5 mAh cm-2 . Moreover, the Na full cell (Na3 V2 (PO4 )3 ||Na2 S/V/Na) exhibits a high energy density of 375 Wh kg-1 and a high power density of 23.5 kW kg-1 . The achievements support the development of heterogeneous protective layers for other high-energy-density metal batteries.

Regulating Li2S Deposition by Ostwald Ripening in Lithium-Sulfur Batteries.

The lithium-sulfur (Li-S) batteries have attracted tremendous attention from both academia and industry for their high energy density and environmental benignity. However, the cell performance suffers from the passivation of the conductive matrix caused by uncontrolled lithium sulfide (Li2S) deposition. Therefore, regulation of Li2S deposition is essential to advanced Li-S batteries. In this work, the role of temperature in regulating Li2S deposition is comprehensively investigated. At room temperature (25 °C), Li2S exhibits a two-dimensional (2D) growth mode. The dense and insulating Li2S film covers the conductive surface rapidly, inhibiting the charge transfer for subsequent polysulfide reduction. Consequently, the severe passivation of the conductive surface degrades the cell performance. In contrast, three-dimensional (3D) Li2S is formed at a high temperature (60 °C) because of a faster Ostwald ripening rate at an elevated temperature. The passivation of the conductive matrix is mitigated effectively, and the cell performance is enhanced significantly, thanks to the formation of 3D Li2S. Ostwald ripening is also valid for Li-S cells under rigorous conditions. The cell working at 60 °C achieves a high specific capacity of 1228 mA h g-1 under the conditions of high S loading and a lean electrolyte (S loading = 3.6 mg cm-2, electrolyte/sulfur ratio = 3 µL mg-1), which is substantially higher than that at 25 °C. This work enriches the intrinsic understanding of Li2S deposition in Li-S batteries and provides facile strategies for improving the cell performance under practical conditions.

Design Principles of Sodium/Potassium Protection Layer for High-Power High-Energy Sodium/Potassium-Metal Batteries in Carbonate Electrolytes: a Case Study of Na2 Te/K2 Te.

The sodium (potassium)-metal anodes combine low-cost, high theoretical capacity, and high energy density, demonstrating promising application in sodium (potassium)-metal batteries. However, the dendrites' growth on the surface of Na (K) has impeded their practical application. Herein, density functional theory (DFT) results predict Na2 Te/K2 Te is beneficial for Na+ /K+ transport and can effectively suppress the formation of the dendrites because of low Na+ /K+ migration energy barrier and ultrahigh Na+ /K+ diffusion coefficient of 3.7 × 10-10 cm2 s-1 /1.6 × 10-10 cm2 s-1 (300 K), respectively. Then a Na2 Te protection layer is prepared by directly painting the nanosized Te powder onto the sodium-metal surface. The Na@Na2 Te anode can last for 700 h in low-cost carbonate electrolytes (1 mA cm-2 , 1 mAh cm-2 ), and the corresponding Na3 V2 (PO4 )3 //Na@Na2 Te full cell exhibits high energy density of 223 Wh kg-1 at an unprecedented power density of 29687 W kg-1 as well as an ultrahigh capacity retention of 93% after 3000 cycles at 20 C. Besides, the K@K2 Te-based potassium-metal full battery also demonstrates high power density of 20 577 W kg-1 with energy density of 154 Wh kg-1 . This work opens up a new and promising avenue to stabilize sodium (potassium)-metal anodes with simple and low-cost interfacial layers.

Electrolyte Solvation Manipulation Enables Unprecedented Room-Temperature Calcium-Metal Batteries.

Calcium-metal batteries (CMBs) provide a promising option for high-energy and cost-effective energy-storage technology beyond the current state-of-the-art lithium-ion batteries. Nevertheless, the development of room-temperature CMBs is significantly impeded by the poor reversibility and short lifespan of the calcium-metal anode. A solvation manipulation strategy is reported to improve the plating/stripping reversibility of calcium-metal anodes by enhancing the desolvation kinetics of calcium ions in the electrolyte. The introduction of lithium salt changes the electrolyte structure considerably by reducing coordination number of calcium ions in the first solvation shell. As a result, an unprecedented Coulombic efficiency of up to 99.1 % is achieved for galvanostatic plating/stripping of the calcium-metal anode, accompanied by a very stable long-term cycling performance over 200 cycles at room temperature. This work may open up new opportunities for development of practical CMBs.

Enabling High-Voltage Lithium Metal Batteries by Manipulating Solvation Structure in Ester Electrolyte.

Lithium metal is an ideal electrode material for future rechargeable lithium metal batteries. However, the widespread deployment of metallic lithium anode is significantly hindered by its dendritic growth and low Coulombic efficiency, especially in ester solvents. Herein, by rationally manipulating the electrolyte solvation structure with a high donor number solvent, enhancement of the solubility of lithium nitrate in an ester-based electrolyte is successfully demonstrated, which enables high-voltage lithium metal batteries. Remarkably, the electrolyte with a high concentration of LiNO3 additive presents an excellent Coulombic efficiency up to 98.8 % during stable galvanostatic lithium plating/stripping cycles. A full-cell lithium metal battery with a lithium nickel manganese cobalt oxide cathode exhibits a stable cycling performance showing limited capacity decay. This approach provides an effective electrolyte manipulation strategy to develop high-voltage lithium metal batteries.

Stable cycling of Na metal anodes in a carbonate electrolyte.

It is significantly challenging to stabilize sodium metal anodes in carbonate electrolytes. Here, we report that a sodium metal anode can achieve a high coulombic efficiency of up to ∼97% over 400 cycles at 0.1 mA cm-2 in a carbonate electrolyte with NaAsF6 as an additive. It is revealed that the SEI layer contains a large amount of NaF and O-As-O polymer which enables the stable cycling of sodium metal anodes.