Designer Cathode Additive for Stable Interphases on High-Energy Anodes

Polymer additives in liquid electrolytes for advanced lithium batteries

Compared to traditional energy storage devices, lithium-ion batteries (LIBs) have the advantages of high energy density, good cycling performance, and low self-discharge rate. Therefore, LIBs have been widely used as the main energy storage devices in various industries. As the blood of the battery, the electrolyte plays a key role in ion transport, formation of the interface layer, protection of electrode materials, etc. The commonly investigated electrolytes include liquid electrolytes, gel electrolytes, and solid or quasi-solid electrolytes. Liquid electrolytes have higher ionic conductivity, which is more conducive to the transport of lithium ions. Therefore, batteries based on liquid electrolytes often exhibit better electrochemical performance. In a liquid electrolyte, the additive is also an indispensable component to ensure the high efficiency of the electrolyte, which plays an important role in regulating the solvation structure of lithium ions, the formation of the solid-electrolyte interface layer, improving the safety performance of batteries, and maintaining operability under extreme conditions (such as low temperature). Unlike previous reviews that focused on small molecule additives, this review herein mainly reviews the application of polymer additives in liquid lithium batteries. Firstly, the functional mechanisms of different types of additives in liquid electrolytesfor lithium batteries are outlined and the advantages and disadvantages of different types of additives are summarized. Then, the research progress of polymers as additives in liquid lithium batteries in recent years is discussed in detail. According to the role of additives, the involved polymer additives are divided into five categories: molecular crowding agents, film-forming agents, HF scavengers, antifreeze agents, and flame retardants. A detailed explanation of the mechanisms related to the efficacy of polymers as additives is also provided. Finally, we present some perspectives on the limitations and future development trends of polymers as additives in liquid lithium batteries and other devices.

Multiscale interfacial stabilization via prelithiation separator engineering for Ah-level anode-free lithium batteries

Anode-free lithium batteries represent a promising avenue for high-energy-density storage, yet their practical application is hindered by lithium inventory loss from parasitic interfacial reactions, cathode degradation, and limited Li+ reversibility. Herein, we propose a polyolefin separator integrated with a Li2S@C sacrificial layer, achieving multiscale interfacial stabilization in Ah-class anode-free pouch cells. This approach simultaneously replenishes the customized Li+ inventory during the formation cycle and establishes the lithium polysulfide-containing cathode interface with high-voltage tolerance (till 4.5 V). Real-time tracking via in-situ electrochemical impedance spectroscopy and transmission-mode operando X-ray diffraction reveals accelerated Li+ diffusion kinetics and stabilized phase evolution in LiNi0.8Co0.1Mn0.1O2 cathode interfaced with Li2S@C|PE prelithiation separator. Consequently, a 1.22 Ah pouch cell with an Ag-modified Cu foil and LiNi0.8Co0.1Mn0.1O2 cathode is assembled with Li2S@C|PE separator and exhibits gravimetric and volumetric energy densities of 450 Wh kg-1 and 1355 Wh L-1, respectively. This prelithiation protocol demonstrates upscaling potential and generic applicability to secure the interfacial chemistries for anode free/less lithium metal batteries.

In-situ positive electrode-electrolyte interphase construction enables stable Ah-level Zn-MnO2 batteries

Engineering the formulation of an Mn-based positive electrode is a viable strategy for producing an efficient aqueous zinc-ion battery. However, Mn dissolution and the byproducts result in capacity fading, thus limiting its electrochemical performances. To solve the undesirable issues, the concept of in-situ forming the positive electrode/electrolyte interface on the commercial MnO2 is designed, with the help of introducing the Dioctyl Phthalate into the ZS-based electrolyte (2 M ZnSO4 + 0.2 M MnSO4), designated as ZS-DOP electrolyte. An advanced three-dimensional chemical and imaging analysis on a model material reveals the dynamic formation of positive electrode/electrolyte interface. The formed organic interface effectively suppresses the corrosion of the electrolytes with its hydrophobicity, and adjusts the pH value according to Le Chatelier's Principle to inhibit the production of by-products. Specifically, the pouch cell assembled with the ZS-DOP electrolyte attains a reversible capacity of ~2.5 Ah and powers the unmanned aerial vehicle. Furthermore, photovoltaic energy storage applications deliver a stable capacity of 0.5 Ah and realize the power supply for mobile phones and other electronic devices. Our results facilitate the development of in-situ surface protection on the positive electrode in aqueous zinc-ion battery, providing insights into its practical application.

Multi layered porous nitrogen-rich biochar materials derived from soybean cellulose for lithium metal anode three-dimensional skeleton in lithium batteries

Lithium metal, renowned for its ultra-high theoretical specific capacity and low electrochemical potential, is a promising anode material for high-energy-density batteries. However, its commercialization is impeded by issues such as uncontrolled Li dendrite growth and volumetric expansion during cycling. Herein, we report the synthesis of a nitrogen- and Si3N4-enriched porous based biochar derived from antibiotic mycelial residues rich in soybean cellulose, which serves as a three-dimensional skeleton for Li metal anodes. This biochar, characterized by a high specific surface area and a porous structure, along with its excellent electrical conductivity, facilitates uniform Li nucleation and growth, thereby mitigating dendrite formation. Results show that the biochar electrode after lithium deposition can achieve stable cycling for over 1200 h at a capacity of 2 mAh cm-2. When integrated with a NCM cathode in a coin cell configuration, the coin-type full cell demonstrates a capacity retention of 85.7 % after 300 cycles at a 0.3C rate. Additionally, pouch cell tests exhibit superior cycling stability with high-capacity retention. This study not only presents an innovative approach to the management of harmful biological waste high in soybean cellulose but also contributes to the advancement of Li metal anode materials for next-generation batteries.

Bio-Inspired Core-Shell Structured Electrode Particles with Protective Mechanisms for Lithium-Ion Batteries

Lithium-ion batteries (LIBs), as predominant energy storage devices, are applied to electric vehicles, which is an effective way to achieve carbon neutrality. However, the major obstructions to their applications are two dilemmas: enhanced cyclic life and thermal stability. Taking advantage of bio-inspired core-shell structures to optimize the self-protective mechanisms of the mercantile electrode particles, LIBs can improve electrochemical performance and thermal stability simultaneously. The favorable core-shell structures suppress volume expansion to stabilize electrode-electrolyte interfaces (EEIs), mitigate direct contact between the electrode material and electrolyte, and promote electrical connectivity. They possess wide operating temperatures, high-voltage resistance, and inhibit short circuits. During cycling, the cathode and anode generate a cathode-electrolyte interface (CEI) and a solid-electrolyte interface (SEI), respectively. Applying multitudinous coating approaches can generate multifarious bio-inspired core-shell structured electrode particles, which is helpful for the generation of the EEIs, self-healing the surface cracks, and maintaining the structural integrities of electrodes. The protected shells act as barriers to minimize unwanted side reactions and enhance thermal stability. These in-depth understandings of the bio-inspired evolution for electrode particles can inspire further enhancements in LIB lifetime and thermal safety, especially for bio-inspired core-shell structured electrodes possessing high-performance protective mechanisms.

Bio-Inspired Electrodes with Rational Spatiotemporal Management for Lithium-Ion Batteries

Lithium-ion batteries (LIBs) are currently the predominant energy storage power source. However, the urgent issues of enhancing electrochemical performance, prolonging lifetime, preventing thermal runaway-caused fires, and intelligent application are obstacles to their applications. Herein, bio-inspired electrodes owning spatiotemporal management of self-healing, fast ion transport, fire-extinguishing, thermoresponsive switching, recycling, and flexibility are overviewed comprehensively, showing great promising potentials in practical application due to the significantly enhanced durability and thermal safety of LIBs. Taking advantage of the self-healing core-shell structures, binders, capsules, or liquid metal alloys, these electrodes can maintain the mechanical integrity during the lithiation-delithiation cycling. After the incorporation of fire-extinguishing binders, current collectors, or capsules, flame retardants can be released spatiotemporally during thermal runaway to ensure safety. Thermoresponsive switching electrodes are also constructed though adding thermally responsive components, which can rapidly switch LIB off under abnormal conditions and resume their functions quickly when normal operating conditions return. Finally, the challenges of bio-inspired electrode designs are presented to optimize the spatiotemporal management of LIBs. It is anticipated that the proposed electrodes with spatiotemporal management will not only promote industrial application, but also strengthen the fundamental research of bionics in energy storage.

Stabilizing the Bulk-Phase and Solid Electrolyte Interphase of Silicon Microparticle Anode by Constructing Gradient-Hierarchically Ordered Conductive Networks

The poor bulk-phase and interphase stability, attributable to adverse internal stress, impede the cycling performance of silicon microparticles (µSi) anodes and the commercial application for high-energy-density lithium-ion batteries. In this work, a groundbreaking gradient-hierarchically ordered conductive (GHOC) network structure, ingeniously engineered to enhance the stability of both bulk-phase and the solid electrolyte interphase (SEI) configurations of µSi, is proposed. Within the GHOC network architecture, two-dimensional (2D) transition metal carbides (Ti3C2Tx) act as a conductive "brick", establishing a highly conductive inner layer on µSi, while the porous outer layer, composed of one-dimensional (1D) Tempo-oxidized cellulose nanofibers (TCNF) and polyacrylic acid (PAA) macromolecule, functions akin to structural "rebar" and "concrete", effectively preserves the tightly interconnected conductive framework through multiple bonding mechanisms, including covalent and hydrogen bonds. Additionally, Ti3C2Tx enhances the development of a LiF-enriched SEI. Consequently, the µSi-MTCNF-PAA anode presents a high discharge capacity of 1413.7 mAh g-1 even after 500 cycles at 1.0 C. Moreover, a full cell, integrating LiNi0.8Mn0.1Co0.1O2 with µSi-MTCNF-PAA, exhibits a capacity retention rate of 92.0% following 50 cycles. This GHOC network structure can offer an efficacious pathway for stabilizing both the bulk-phase and interphase structure of anode materials with high volumetric strain.

Designer Lithium Reservoirs for Ultralong Life Lithium Batteries for Grid Storage

The minimization of irreversible active lithium loss stands as a pivotal concern in rechargeable lithium batteries, particularly in the context of grid-storage applications, where achieving the utmost energy density over prolonged cycling is imperative to meet stringent demands, notably in terms of life cost. Departing from conventional methodologies advocating electrode prelithiation and/or electrolyte additives, a new paradigm is proposed here: the integration of a designer lithium reservoir (DLR) featuring lithium orthosilicate (Li4SiO4) and elemental sulfur. This approach concurrently addresses active lithium consumption through solid electrolyte interphase (SEI) formation and mitigates minor yet continuous parasitic reactions at the electrode/electrolyte interface during extended cycling. The remarkable synergy between the Li-ion conductive Li4SiO4 and the SEI-favorable elemental sulfur enables customizable compensation kinetics for active lithium loss throughout continuous cycling. The introduction of a minute quantity of DLR (3 wt% Li4SiO4@S) yields outstanding cycling stability in a prototype pouch cell (graphite||LiFePO4) with an ampere-hour-level capacity (≈2.3 Ah), demonstrating remarkable capacity retention (≈95%) even after 3000 cycles. This utilization of a DLR is poised to expedite the development of enduring lithium batteries for grid-storage applications and stimulate the design of practical, implantable rechargeable batteries based on related cell chemistries.

A Room-Temperature Self-Healing Liquid Metal-Infilled Microcapsule Driven by Coaxial Flow Focusing for High-Performance Lithium-Ion Battery Anode

Liquid metals have attracted a lot of attention as self-healing materials in many fields. However, their applications in secondary batteries are challenged by electrode failure and side reactions due to the drastic volume changes during the "liquid-solid-liquid" transition. Herein, a simple encapsulated, mass-producible method is developed to prepare room-temperature liquid metal-infilled microcapsules (LMMs) with highly conductive carbon shells as anodes for lithium-ion batteries. Due to the reasonably designed voids in the microcapsule, the liquid metal particles (LMPs) can expand freely without damaging the electrode structure. The LMMs-based anodes exhibit superior capacity of rete-performance and ultra-long cycling stability remaining 413 mAh g-1 after 5000 cycles at 5.0 A g-1. Ex situ X-ray powder diffraction (XRD) patterns and electrochemical impedance spectroscopy (EIS) reveal that the LMMs anode displays a stable alloying/de-alloying mechanism. DFT calculations validate the electronic structure and stability of the room-temperature LMMs system. These findings will bring some new opportunities to develop high-performance battery systems.

A Fast Na-Ion Conduction Polymer Electrolyte via Triangular Synergy Strategy for Quasi-Solid-State Batteries

Polymer electrolytes provide a visible pathway for the construction of high-safety quasi-solid-state batteries due to their high interface compatibility and processability. Nevertheless, sluggish ion transfer at room temperature seriously limits their applications. Herein, a triangular synergy strategy is proposed to accelerate Na-ion conduction via the cooperation of polymer-salt, ionic liquid, and electron-rich additive. Especially, PVDF-HFP and NaTFSI salt acted as the framework to stably accommodate all the ingredients. An ionic liquid (Emim+ -FSI- ) softened the polymer chains through a weakening molecule force and offered additional liquid pathways for ion transport. Physicochemical characterizations and theoretical calculations demonstrated that electron-rich Nerolin with π-cation interaction facilitated the dissociation of NaTFSI and effectively restrained the competitive migration of large cations from EmimFSI, thus lowering the energy barrier for ion transport. The strategy resulted in a thin F-rich interphase dominated by NaTFSI salt's decomposition, enabling rapid Na+ transmission across the interface. These combined effects resulted in a polymer electrolyte with high ionic conductivity (1.37×10-3  S cm-1 ) and tNa+ (0.79) at 25 °C. The assembled cells delivered reliable rate capability and stability (200 cycles, 99.2 %, 0.5 C) with a good safety performance.

Domino Reactions Enabling Sulfur-Mediated Gradient Interphases for High-Energy Lithium Batteries

Silicon (Si)-based anodes are currently considered a feasible solution to improve the energy density of lithium-ion batteries owing to their sufficient specific capacity and natural abundance. However, Si-based anodes exhibit low electric conductivities and large volume changes during cycling, which could easily trigger continuous breakdown/reparation of the as-formed solid-electrolyte-interphase (SEI) layer, seriously hampering their practical application in current battery technology. To control the chemoelectrochemical instability of the conventional SEI layer, we herein propose the introduction of elemental sulfur into nonaqueous electrolytes, aiming to build a sulfur-mediated gradient interphase (SMGI) layer on Si-based anodes. The SMGI layer is generated through the domino reactions (i.e., electrochemical cascade reactions) involving the electrochemical reductions of elemental sulfur followed by nucleophilic substitutions of fluoroethylene carbonate, which endows the corresponding SEI layer with strong elasticity and chemomechanical stability and enables rapid transportation of Li+ ions. Consequently, the prototype Si||LiNi0.8Co0.1Mn0.1O2 cells attain a high-energy density of 622.2 W h kg-1 and a capacity retention of 88.8% after 100 cycles. Unlike previous attempts based on sophisticated chemical modifications of electrolyte components, this study opens a new avenue in interphase design for long-lived and high-energy rechargeable batteries.

Significantly Improving the Initial Coulombic Efficiency of TiO2 Anode for Sodium-Ion Batteries

Titanium dioxide (TiO2) can serve as a candidate anode material for sodium-ion batteries (SIBs) with the merits of their low cost, abundance, and environment friendliness. However, its low initial Coulombic efficiency (ICE) and sluggish sodium-ion diffusion greatly limit its further practical applications. Herein, we report a one-step prepotassiation strategy to modify commercial TiO2 by a spontaneous chemical reaction using potassium naphthalene (K-Nt). Prepotassiation effectively compensates for the irreversible Na loss and induces a homogeneous, dense, and robust artificial solid electrolyte interphase (SEI) on its surface. The well-distributed artificial SEI suppresses the excessive electrolyte decomposition, contributing to rapid interfacial kinetics and stable Na+ insertion/extraction. Therefore, such modified commercial TiO2 anodes demonstrate significantly improved ICE (72.4%) and outstanding rate performance (176.4 mAh g-1 at 5 A g-1). This simple and efficient method for promoting ICEs and interfacial chemistry also demonstrates universality and practical value for other anodes in SIBs.