Limited Lithium Loading Promises Improved Lithium-Metal Anodes in Interface-Modified 3D Matrixes

Recent Progress on the Air-Stable Battery Materials for Solid-State Lithium Metal Batteries

Solid-state lithium metal batteries (SSLMBs) offer numerous advantages in terms of safety and theoretical specific energy density. However, their main components namely lithium metal anode, solid-state electrolyte, and cathode, show chemical instability when exposed to humid air, which results in low capacities and poor cycling stability. Recent studies have shown that bioinspired hydrophobic materials with low specific surface energies can protect battery components from corrosion caused by humid air. Air-stable inorganic materials that densely cover the surface of battery components can also provide protection, which improves the storage stability of the battery components, broadens their processing conditions, and ultimately decreases their processing costs while enhancing their safety. In this review, the mechanism behind the surface structural degradation of battery components and the resulting consequences are discussed. Subsequently, recent strategies are reviewed to address this issue from the perspectives of lithium metal anodes, solid-state electrolytes, and cathodes. Finally, a brief conclusion is provided on the current strategies and fabrication suggestions for future safe air-stable SSLMBs.

Highly Reversible Lithium-Ion Battery with Excellent Rate Performance and Cycle Stability Based on a Ti3C2/CoS2 Composite Anode

Transition metal sulfide (TMS) CoS2 is considered an ideal anode material for new-generation lithium-ion batteries (LIBs) because of its high specific capacity, high electrochemical activity, and low cost. However, CoS2 is prone to volume expansion and structural collapse when it participates in the internal conversion reaction of the battery, which limits its practical application. After analyzing the failure mechanism of CoS2 as the anode material of LIBs, the concept of nanoengineered materials is introduced here. CoS2 particles are nanosized and stabilized by constructing a composite structure on an alkali-treated two-dimensional Ti3C2 Mxene conductive network. Both experiments and theoretical calculations show that special Ti-O-Co bonds are formed at the interface of the Ti3C2/CoS2 composite through oxygen-containing functional groups. Ti-O-Co bonding with adjustable electronic characteristics can effectively promote the utilization rate of anode materials, electronic conductivity, and ionic diffusivity and thus enhance the redox reaction kinetics of the device. When the Ti3C2/CoS2 composite is used as the anode material for LIBs, it still provides a high specific capacity of 405.8 mAh g-1 after 100 cycles at 0.1 A g-1. After running for 1000 cycles at a high current of 1 A g-1, the capacity retention is still close to 100%. Also, high cycle stability under the condition of highly active material loading (10.58 mg cm-2) and low electrolyte/active material ratio (10 μL mg-1) is achieved. This work provides a new idea for the development of commercial LIBs as anode materials.

Nitrogen Ion Implantation-Modified Cu Substrate for Stable Lithium Metal Anode

As the only commercialized negative current collector, copper (Cu) foil possesses insurmountable applicational advantages as a lithium metal anode (LMA) substrate. However, the successful usage of Cu foil is limited by the poor Li affinity and crystal face variation, which will lead to severe lithium dendrite growth and poor cyclability. Herein, an industrial-popular ion implantation technique is first adopted for Cu surface modification. With the high-energy implantations of N+ plasma, the unique N-rich transition interface can be formed, among which the lithiophilic CuxNy with extended crystal domains can have uniform Cu crystal faces and offer benefit for Li nucleation/deposition; besides, the induced Li3N-rich SEI with high ionic conductivity can support Li-ion transport kinetics, suppress Li dendrite growth, and mitigate the side reaction to improve LMA stability. Consequently, a uniform Li nucleation/deposition is achieved, with obviously enhanced cycling stability and rate capability for the full cells. This technological maturity ion implantation method can be readily extended to any non/metallic ion species, or joint implantation of bi/multiple ions, and other substrates, demonstrating a possible route to surmount the metal anode challenges.

Ultrathin Li-rich Li-Cu alloy anode capped with lithiophilic LiC6 headspace enabling stable cyclic performance

Li-rich dual-phase Li-Cu alloy is a promising candidate toward practical application of Li metal anode due to its in situ formed unique three-dimensional (3D) skeleton of electrochemical inert LiCu_x solid-solution phase. Since a thin layer of metallic Li phase appears on the surface of as-prepared Li-Cu alloy, the LiCu_x framework cannot regulate Li deposition efficiently in the first Li plating process. Herein, a lithiophilic LiC₆ headspace is capped on the upper surface of the Li-Cu alloy, which can not only offer free space to accommodate Li deposition and maintain dimensional stability of the anode, but also provide abundant lithiophilic sites and guide Li deposition effectively. This unique bilayer architecture is fabricated via a facile thermal infiltration method, where the Li-Cu alloy layer with an ultrathin thickness around 40 μm occupies the bottom of a carbon paper (CP) sheet, and the upper part of this 3D porous framework is reserved as the headspace for Li storage. Notably, the molten Li can quickly convert these carbon fibers of the CP into lithiophilic LiC₆ fibers while the CP is touched with the liquid Li. The synergetic effect between the LiC₆ fibers framework and LiCu_x nanowires scaffold can ensure a uniform local electric field and stable Li metal deposition during cycling. As a consequence, the CP capped ultrathin Li-Cu alloy anode demonstrates excellent cycling stability and rate capability.

Deciphering the Dynamic Processes at the Electrode-Electrolyte Interface for Stable Deposition of Lithium

Realization of lithium-metal (Li) batteries is plagued by the dendritic deposition of Li leading to internal short-circuit and low Coulombic efficiency. The Li-deposition process largely depends on the liquid electrolyte that reacts with the Li metal and forms a solid electrolyte interphase (SEI) layer with diverse chemical and physical properties. Moreover, the electrolyte possesses characteristic ion transport behaviors and directly affects the deposition kinetics at the electrode surface. As a result, the convolution of interfacial, ion transport, and kinetic effects of an electrolyte obscures the understanding of Li deposition in Li-metal batteries. Herein, the dynamic processes and the interfacial properties of Li-metal electrodes are precisely delineated in representative ether electrolytes. It is found that a combination of homogeneous SEI and slow deposition kinetics produces layer-by-layer epitaxial growth of Li. In contrast, the dendritic growth of Li is observed when the SEI is inhomogeneous and the reaction rate is fast. Nevertheless, it is shown that a homogeneous SEI is not a prerequisite in suppressing Li dendrites when the adverse effect of an unfavorable SEI can be subdued by proper kinetic tuning at the interface. Furthermore, an otherwise kinetically unstable electrolyte can also be made compatible with the Li-metal electrode when covered with a properly designed SEI. This delineation of the roles of SEI and deposition kinetics gives deep insight into designing efficient electrolytes in Li-metal batteries.