Rui Wen

A Flexible Solid Electrolyte Interphase Layer for Long-Life Lithium Metal Anodes

Lithium (Li) metal is a promising anode material for high-energy density batteries. However, the unstable and static solid electrolyte interphase (SEI) can be destroyed by the dynamic Li plating/stripping behavior on the Li anode surface, leading to side reactions and Li dendrites growth. Herein, we design a smart Li polyacrylic acid (LiPAA) SEI layer high elasticity to address the dynamic Li plating/stripping processes by self-adapting interface regulation, which is demonstrated by in situ AFM. With the high binding ability and excellent stability of the LiPAA polymer, the smart SEI can significantly reduce the side reactions and improve battery safety markedly. Stable cycling of 700 h is achieved in the LiPAA-Li/LiPAA-Li symmetrical cell. The innovative strategy of self-adapting SEI design is broadly applicable, providing opportunities for use in Li metal anodes.

Insight into the Interfacial Process and Mechanism in Lithium-Sulfur Batteries: An In Situ AFM Study.

Lithium-sulfur (Li-S) batteries are highly appealing for large-scale energy storage. However, performance deterioration issues remain, which are highly related to interfacial properties. Herein, we present a direct visualization of the interfacial structure and dynamics of the Li-S discharge/charge processes at the nanoscale. In situ atomic force microscopy and ex situ spectroscopic methods directly distinguish the morphology and growth processes of insoluble products Li2 S2 and Li2 S. The monitored interfacial dynamics show that Li2 S2 nanoparticle nuclei begin to grow at 2 V followed by a fast deposition of lamellar Li2 S at 1.83 V on discharge. Upon charging, only Li2 S depletes from the interface, leaving some Li2 S2 undissolved, which accumulates during cycling. The galvanostatic precipitation of Li2 S2 and/or Li2 S is correlated to current rates and affects the specific capacity. These findings reveal a straightforward structure-reactivity correlation and performance fading mechanism in Li-S batteries.

Dendrite-Free Li-Metal Battery Enabled by a Thin Asymmetric Solid Electrolyte with Engineered Layers

The key bottleneck troubling the application of solid electrolyte is the contradictory requirements from Li-metal and cathode, which need high modulus to block Li-dendrite penetration and flexibility to enable low interface resistance, respectively. This study describes a thin asymmetrical design of solid electrolyte to address these shortcomings. In this architecture, a rigid ceramic-layer modified with an ultrathin polymer is toward Li-metal to accomplish dendrite-suppression of Li-anode, and a soft polymer-layer spreads over the exterior and interior of cathode to endow connected interface simultaneously. This ingenious arrangement endows solid Li-metal batteries with extremely high Coulombic efficiency and cyclability. This work will open up one avenue for realizing safe and long-life energy storage systems.

Direct Visualization of Nucleation and Growth Processes of Solid Electrolyte Interphase Film Using in Situ Atomic Force Microscopy

An understanding of the formation mechanism of solid electrolyte interphase (SEI) film at the nanoscale is paramount because it is one of the key issues at interfaces in lithium-ion batteries (LIBs). Herein, we explored the nucleation, growth, and formation of SEI film on highly oriented pyrolytic graphite (HOPG) substrate in ionic liquid-based electrolytes 1-butyl-1-methyl-pyrrolidinium bis(fluorosulfonyl)imide ([BMP]+[FSI]-) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([BMP]+[TFSI]-) by in situ atomic force microscopy (AFM) and found that the types of anions have significant influence on the structure of the formed SEI. In [BMP]+[FSI]- containing LiFSI, a compact and thin SEI film prefers to grow in the plane of HOPG substrate, while a rough and loose film tends to form in [BMP]+[TFSI]- containing LiTFSI. On the basis of in situ AFM observations, the relationship between the SEI structure and the electrochemical performance was clarified.

Interfacial Mechanism in Lithium–Sulfur Batteries: How Salts Mediate the Structure Evolution and Dynamics

Lithium-sulfur batteries possess favorable potential for energy-storage applications because of their high specific capacity and the low cost of sulfur. Intensive understanding of the interfacial mechanism, especially the polysulfide formation and transformation under complex electrochemical environment, is crucial for the buildup of advanced batteries. Here, we report the direct visualization of interfacial evolution and dynamic transformation of the sulfides mediated by the lithium salts via real-time atomic force microscopy monitoring inside a working battery. The observations indicate that the lithium salts influence the structures and processes of sulfide deposition/decomposition during discharge/charge. Moreover, the distinct ion interaction and the diffusion in electrolytes manipulate the interfacial reactions determining the kinetics of the sulfide transformation. Our findings provide deep insights into surface dynamics of lithium-sulfur reactions revealing the salt-mediated mechanisms at nanoscale, which contribute to the profound understanding of the interfacial processes for the optimized design of lithium-sulfur batteries.

High‐Temperature Formation of a Functional Film at the Cathode/Electrolyte Interface in Lithium–Sulfur Batteries: An In Situ AFM Study

Lithium-sulfur (Li-S) batteries have been attracting wide attention due to their promising high specific capacity. Deep understanding of Li-S interfacial mechanism including the temperature (T) effect is increasingly required to meet the burgeoning demands for battery modification and systematic researches. Herein, interfacial behavior during discharge/charge is investigated at high temperature (HT) of 60 C in electrolyte based on lithium bis(fluorosulfonyl) imide (LiFSI). By in situ atomic force microscopy (AFM), dynamic evolution of insoluble Li2S2 and Li2S is studied at the nanoscale. An in situ formed protective film can be directly monitored at 60 C after Li2S nucleation, retarding side reactions and facilitating interfacial redox. The deep insight into the interfacial processes at HT discovers a direct evidence of the existence of the protective film and reveals its dynamic behaviors, providing a new avenue for electrolyte design and performance enhancement with a long span.

Gradiently Polymerized Solid Electrolyte Meets with Micro-/Nanostructured Cathode Array

The poor contact between the solid-state electrolyte and cathode materials leads to a high interfacial resistance, severely limiting the rate capability of solid Li metal batteries. Herein, an integrative battery design is introduced with a gradiently polymerized solid electrolyte (GPSE), a microchannel current collector array, and nanosized cathode particles. An in situ formed GPSE encapsulates cathode nanoparticles in the microchannel with ductile inclusions to lower the interfacial impedance, and the stiff surface layer of GPSE toward anode suppresses the Li dendrite growth. The Li metal batteries based on GPSE and the Li-free hydrogenated V2O5 (V2O5-H) cathode exhibit an outstanding high rate response of up to 5 C (the capacity ratio of 5 C/1 C is 90.3%) and an ultralow capacity fade rate of 0.07% per cycle over 300 cycles. The other Li-containing cathodes such as LiFePO4 and LiNi0.5Mn0.3Co0.2O2 can also operate effectively at the rates of 5 and 2 C, respectively. Such an ingenious design may provide new insights into other solid metal batteries through an interfacial engineering manipulation at the micro- and nanolevel.

Constructing a Stable Lithium Metal–Gel Electrolyte Interface for Quasi-Solid-State Lithium Batteries

Interfacial problems, including interfacial stability and contact issues, severely plague the practical application of Li metal anodes. Here we report an interfacial regulation strategy that stabilizes the Li metal-gel electrolyte interface through in situ constructing a stable solid electrolyte interphase (SEI) layer. By stabilizing the interface of Li metal anodes, the gel electrolyte enables dendrite-free morphology and high plating/stripping efficiency. A systematic analysis further confirms that the formed SEI layer is responsible for homogeneous deposition and stable cycling performance. Benefiting from the interfacial stability between electrodes and electrolytes, the lifespan of Li metal batteries is extended.