Design of a Multifunctional Interlayer for NASCION-Based Solid-State Li Metal Batteries

NASCION-type Li conductors have great potential to bring high capacity solid-state batteries to realization, related to its properties such as high ionic conductivity, stability under ambient conditions, wide electrochemical stability window, and inexpensive production. However, their chemical and thermal instability toward metallic lithium (Li) has severely hindered attempts to utilize Li as anode material in NASCION-based battery systems. In this work, it is shown how a tailored multifunctional interlayer between the solid electrolyte and Li anode can successfully address the interfacial issues. This interlayer is designed by creating a quasi-solid-state paste in which the functionalities of LAGP (Li1.5Al0.5Ge1.5(PO4)3) nanoparticles and an ionic liquid (IL) electrolyte are combined. In a solid-sate cell, the LAGP-IL interlayer separates the Li metal from bulk LAGP and creates a chemically stable interface with low resistance (≈5 Ω cm2) and efficiently prevents thermal runaway at elevated temperatures (300 \ub0C). Solid-state cells designed with the interlayer can be operated at high current densities, 1 mA cm−2, and enable high rate capability with high safety. Here developed strategy provides a generic path to design interlayers for solid-state Li metal batteries

Insight into the Critical Role of Exchange Current Density on Electrodeposition Behavior of Lithium Metal

Due to an ultrahigh theoretical specific capacity of 3860 mAh g−1, lithium (Li) is regarded as the ultimate anode for high-energy-density batteries. However, the practical application of Li metal anode is hindered by safety concerns and low Coulombic efficiency both of which are resulted fromunavoidable dendrite growth during electrodeposition. This study focuses on a critical parameter for electrodeposition, the exchange current density, which has attracted only little attention in research on Li metal batteries. A phase-field model is presented to show the effect of exchange current density on electrodeposition behavior of Li. The results show that a uniform distribution of cathodic current density, hence uniform electrodeposition, on electrode is obtained with lower exchange current density. Furthermore, it is demonstrated that lower exchange current density contributes to form a larger critical radius of nucleation in the initial electrocrystallization that results in a dense deposition of Li, which is a foundation for improved Coulombic efficiency and dendrite-free morphology. The findings not only pave the way to practical rechargeable Li metal batteries but can also be translated to the design of stable metal anodes, e.g., for sodium (Na), magnesium (Mg), and zinc (Zn) batteries

Structural Origin of Suppressed Voltage Decay in Single‐Crystalline Li‐Rich Layered Li[Li0.2_{0.2}Ni0.2_{0.2}Mn0.6_{0.6}]O2_{2} Cathodes

Lithium- and manganese-rich layered oxides (LMLOs, ≥ 250 mAh g$^{−1}$) with polycrystalline morphology always suffer from severe voltage decay upon cycling because of the anisotropic lattice strain and oxygen release induced chemo-mechanical breakdown. Herein, a Co-free single-crystalline LMLO, that is, Li[Li$_{0.2}$Ni$_{0.2}$Mn$_{0.6}$]O$_{2}$ (LLNMO-SC), is prepared via a Li$^+$/Na$^+$ ion-exchange reaction. In situ synchrotron-based X-ray diffraction (sXRD) results demonstrate that relatively small changes in lattice parameters and reduced average micro-strain are observed in LLNMO-SC compared to its polycrystalline counterpart (LLNMO-PC) during the charge–discharge process. Specifically, the as-synthesized LLNMO-SC exhibits a unit cell volume change as low as 1.1% during electrochemical cycling. Such low strain characteristics ensure a stable framework for Li-ion insertion/extraction, which considerably enhances the structural stability of LLNMO during long-term cycling. Due to these peculiar benefits, the average discharge voltage of LLNMO-SC decreases by only ≈0.2 V after 100 cycles at 28 mA g$^{-1}$ between 2.0 and 4.8 V, which is much lower than that of LLNMO-PC (≈0.5 V). Such a single-crystalline strategy offers a promising solution to constructing stable high-energy lithium-ion batteries (LIBs)

Stable Li metal anode by crystallographically oriented plating through in-situ surface doping

Lithium (Li) metal is regarded as the holy grail anode material for high-energy-density batteries owing to its ultrahigh theoretical specific capacity. However, its practical application is severely hindered by the high reactivity of metallic Li against the commonly used electrolytes and uncontrolled growth of mossy/dendritic Li. Different from widely-used approaches of optimization of the electrolyte and/or interfacial engineering, here, we report a strategy of in-situ cerium (Ce) doping of Li metal to promote the preferential plating along the [200] direction and remarkably decreased surface energy of metallic Li. The in-situ Ce-doped Li shows a significantly reduced reactivity towards a standard electrolyte and, uniform and dendrite-free morphology after plating/stripping, as demonstrated by spectroscopic, morphological and electrochemical characterizations. In symmetric half cells, the in-situ Ce-doped Li shows a low corrosion current density against the electrolyte and drastically improved cycling even at a lean electrolyte condition. Furthermore, we show that the stable Li LiCoO2 full cells with improved coulombic efficiency and cycle life are also achieved using the Ce-doped Li metal anode. This work provides an inspiring approach to bring Li metal towards practical application in high energy-density batteries

In Situ Volume Change Studies of Lithium Metal Electrode under Different Pressure

Due to the high theoretical capacity density of 3680 mAh g(-1), lithium (Li) is considered as a promising anode for high-energy-density battery systems. However, its practical application is severely hampered by the invariable growth of Li dendrites and tremendous volume change during electrochemical plating-stripping process. Although real-time monitoring of the volume change is crucial for research and development of stable lithium anode, the studies are rare due to the lack of in-situ swelling equipment so far. Here, we report an in-situ volume change system to observe the thickness change of Li electrode at a resolution of micrometer during the electrochemical process. With a comprehensive design for this instrument, a continuously tunable pressure can be applied on the Li-Li symmetric cell to investigate the impact of pressure on the stability of Li electrode during cycling. We found that the higher pressure (similar to 850kPa) is beneficial for stabilizing Li electrode during plating/stripping process. Our results provide a perspective to investigate the electrochemical behavior of Li electrode. In addition, this instrument also shows great potential of in-situ volume change monitoring in other battery systems like silicon anode and solid-state batteries

Enhanced ionic conductivity and interface stability of hybrid solid-state polymer electrolyte for rechargeable lithium metal batteries

Compared to conventional organic liquid electrolyte, solid-state polymer electrolytes are extensively considered as an alternative candidate for next generation high-energy batteries because of their high safety, non-leakage and electrochemical stability with the metallic lithium (Li) anode. However, solid-state polymer electrolytes generally show low ionic conductivity and high interfacial impedance to electrodes. Here we report a hybrid solid-state electrolyte, presenting an ultra-high ionic conductivity of 3.27 mS cm −1 at room temperature, a wide electrochemical stability window of 4.9 V, and non-flammability. This electrolyte consists of a polymer blend matrix (polyethylene oxide and poly (vinylidene fluoride-co-hexafluoropropylene)), Li + conductive ceramic filler (Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 ) and a solvate ionic liquid (LiFSI in tetra ethylene glycol dimethyl ether, 1:1 in molar ratio) as plasticizer. The introduction of the solvate ionic liquid to the solid-state electrolyte not only improves its ionic conductivity but also remarkably enhances the stability of the interface with Li anode. When applied in Li metal batteries, a Li|Li symmetric cell can operate stably over 800 h with a minimal polarization of 25 mV and a full Li|LiFePO 4 cell delivers a high specific capacity of 158 mAh g −1 after 100 cycles at room temperature

Electrochemically Induced Defects Promotional High-Performance Binder-Free MnO@CC Cathodes for Flexible Quasi-Solid-State Zinc-Ion Battery

Aqueous Zn-ion batteries (ZIBs) have attracted ever-increasing attention because of their features of a cheaper cost, high safety level, and environment protection. Manganese-based oxides stand out among the many cathode material candidates because of their high voltage platform (1.4 V vs Zn2+/Zn). Nevertheless, manganese ion dissolution still is an essential issue in the application of manganese-based cathodes, and the strategy of using manganese ion dissolution to activate electrode materials is rarely achieved. Here, a high-capacity and stable binder-free MnO@CC cathode was prepared by facile electrochemical deposition and carbothermal reduction methods. Based on the MnO@CC cathode and a homemade gel polymer electrolyte, a flexible quasi-solid state ZIB was assembled and exhibited a high reversible capacity, a significant energy output of 345 Wh kg–1, and excellent long-term cycling performance. The ultradispersed and well-crystallized octahedral MnO nanoparticle provides an improved ion transfer interface, and abundant Mn vacancy during the initial charging process provides sufficient inserted channels and available active sites for subsequent ion insertion and storage. In addition, for the as-activated MnO@CC electrode, the reversible coinsertion mechanism (H+ and Zn2+) is also monitored in the aqueous ZIBs. This work may provide insights into manufacturing advanced flexible aqueous ZIBs for wearable electronics via defect engineering