Solid Electrolyte Interphase Research Articles

Amorphous shear band formation in crystalline Si-anodes governs lithiation and capacity fading in Li-ion batteries

The cycling stability of Li-ion batteries is commonly attributed to the formation of the solid electrolyte interphase (SEI) layer, which is generated on the active material surface during electrochemical reactions in battery operation. Silicon experiences large volume changes upon the Li-insertion and extraction, leading to the amorphization of the silicon-interface due to the permeation of the Li-ions into the silicon. Here, we discover how generated non-hydrostatic strain upon electrochemical cycling further triggers dislocation and eventually shear band formation within the crystalline silicon core. The latter boosts the non-uniform lithiation at the silicon interface affecting the SEI reformation process and ultimately the capacity. Our findings are based on a comprehensive multiscale structural and chemical experimental characterization, complemented by molecular dynamics modelling. This approach highlights the importance of considering electrochemical, microstructural and mechanical mechanisms, offering a strategy for developing improved anode materials with enhanced cycling stability and reduced capacity loss.

Deciphering the Decomposition Mechanisms of Ether and Fluorinated Ether Electrolytes on Lithium Metal Surfaces: Insights from CMD and AIMD Simulations.

The performance of lithium metal batteries can be significantly enhanced by incorporating fluorinated ether-based electrolytes, yet the solid electrolyte interphase (SEI) formation mechanism on lithium metal surfaces remains elusive. This study employs classical and ab initio molecular dynamics simulations to investigate the decomposition mechanisms of lithium bis(fluoromethanesulfonyl)imide (LiFSI) in 1,2-diethoxyethane (DEE) and its fluorinated analogues, F5DEE and F2DEE, when in contact with lithium metal. Our findings indicate that F5DEE-based electrolytes favor the formation of a FSI-rich primary solvation shell around Li+, while F2DEE-based electrolytes yield a solvent-rich environment. The normalized number density at the Li/electrolyte/Li interface shows a depletion of FSI anions in the electrochemical double layer (EDL) structure near the Li anode upon charging, with the distance between the first main peak of the FSI anion and Li anode following the order F5DEE < DEE < F2DEE. Analysis of the electronic projected density of states and charge transfer dynamics unveils the reductive dissociation pathways of FSI anions and fluorinated DEE solvents on the lithium metal surface, taking into account the influence of the EDL structure. DEE is identified as the most reduction-stable solvent, leading to the selective dissociation of FSI anions and the formation of an entirely inorganic SEI. In contrast, F2DEE displays a pronounced reduction tendency, forming an organic-rich SEI due to the solvent-dominated lowest unoccupied molecular orbital at the interface. F5DEE, competing with FSI anions for reduction, results in the formation of an inorganic-rich hybrid SEI with the highest LiF content. The simulation results correlate well with experimental observations and underscore the pivotal role of various fluorinated functional groups in the formation of EDL and SEI near the lithium metal surface.

Quantification of Charge Transport and Mass Deprivation in Solid Electrolyte Interphase for Kinetically‐Stable Low‐Temperature Lithium‐Ion Batteries

AbstractGraphite (Gr)‐based lithium‐ion batteries with admirable electrochemical performance below −20 °C are desired but are hindered by sluggish interfacial charge transport and desolvation process. Li salt dissociation via Li+‐solvent interaction enables mobile Li+ liberation and contributes to bulk ion transport, while is contradictory to fast interfacial desolvation. Designing kinetically‐stable solid electrolyte interphase (SEI) without compromising strong Li+‐solvent interaction is expected to compatibly improve interfacial charge transport and desolvation kinetics. However, the relationship between physicochemical features and temperature‐dependent kinetics properties of SEI remains vague. Herein, we propose four key thermodynamics parameters of SEI potentially influencing low‐temperature electrochemistry, including electron work function, Li+ transfer barrier, surface energy, and desolvation energy. Based on the above parameters, we further define a novel descriptor, separation factor of SEI (SSEI), to quantitatively depict charge (Li+/e−) transport and solvent deprivation processes at Gr/electrolyte interface. A Li3PO4‐based, inorganics‐enriched SEI derived by Li difluorophosphate (LiDFP) additive exhibits the highest SSEI (4.89×103) to enable efficient Li+ conduction, e− blocking and rapid desolvation, and as a result, much suppressed Li‐metal precipitation, electrolyte decomposition and Gr sheets exfoliation, thus improving low‐temperature battery performances. Overall, our work originally provides visualized guides to improve low‐temperature reaction kinetics/thermodynamics by constructing desirable SEI chemistry.

Quantification of Charge Transport and Mass Deprivation in Solid Electrolyte Interphase for Kinetically-Stable Low-Temperature Lithium-Ion Batteries.

Graphite (Gr)-based lithium-ion batteries with admirable electrochemical performance below -20 °C are desired but are hindered by sluggish interfacial charge transport and desolvation process. Li salt dissociation via Li+-solvent interaction enables mobile Li+ liberation and contributes to bulk ion transport, while is contradictory to fast interfacial desolvation. Designing kinetically-stable solid electrolyte interphase (SEI) without compromising strong Li+-solvent interaction is expected to compatibly improve interfacial charge transport and desolvation kinetics. However, the relationship between physicochemical features and temperature-dependent kinetics properties of SEI remains vague. Herein, we propose four key thermodynamics parameters of SEI potentially influencing low-temperature electrochemistry, including electron work function, Li+ transfer barrier, surface energy, and desolvation energy. Based on the above parameters, we further define a novel descriptor, separation factor of SEI (SSEI), to quantitatively depict charge (Li+/e-) transport and solvent deprivation processes at Gr/electrolyte interface. A Li3PO4-based, inorganics-enriched SEI derived by Li difluorophosphate (LiDFP) additive exhibits the highest SSEI (4.89×103) to enable efficient Li+ conduction, e- blocking and rapid desolvation, and as a result, much suppressed Li-metal precipitation, electrolyte decomposition and Gr sheets exfoliation, thus improving low-temperature battery performances. Overall, our work originally provides visualized guides to improve low-temperature reaction kinetics/thermodynamics by constructing desirable SEI chemistry.

In Situ Analysis of Interfacial Morphological and Chemical Evolution in All-Solid-State Lithium-Metal Batteries.

In situ analysis of Li plating/stripping processes and evolution of solid electrolyte interphase (SEI) are critical for optimizing all-solid-state Li metal batteries (ASSLMB). However, the buried solid-solid interfaces present a challenge for detection which preclude the employment of multiple analysis techniques. Herein, by employing complementary in situ characterizations, morphological/chemical evolution, Li plating/stripping dynamics and SEI dynamics were directly detected. As a mixed ionic-electronic conducting interface, Li|Li10GeP2S12 (LGPS) performed distinct interfacial morphological/chemical evolution and dynamics from ionic-conducting/electronic-isolating interface like Li|Li3PS4 (LPS), which were revealed by combination of in situ atomic force microscopy and in situ X-ray photoelectron spectroscopy. Though Li plating speed in LGPS was higher than LPS, speed of SSE decomposition was similar and ~85 % interfacial SSE turned into SEI during plating and remained unchanged in stripping. To leverage strengths of different SSEs, an LPS-LGPS-LPS sandwich electrolyte was developed, demonstrating enhanced ionic conductivity and improved interfacial stability with less SSE decomposition (25 %). Using in situ Kelvin probe force microscopy, Li-ion behavior at interface between different SSEs was effectively visualized, uncovering distribution of Li ions at LGPS|LPS interface under different potentials.

New Nitrate Additive Enabling Highly Stable and Conductive SEI for Fast‐Charging Lithium Metal Batteries

AbstractPolyester‐based electrolytes formed via in situ polymerization, have been regarded as one of the most promising solid electrolyte systems. Nevertheless, it is still a great challenge to address the issue of their high reactivity with metallic lithium anode by optimizing the components and properties of solid electrolyte interphase (SEI). Herein, a new class of N‐containing additive, isopropyl nitrate (ISPN) that can be miscible with ester solvents is demonstrated, and a chemically stable and ion‐conductive LiF‐Li3N composite SEI is constructed. In addition, ISPN can induce the formation of anion‐enriched solvation structures and reduces the desolvation barrier of Li+, resulting in fast transport of Li+. With the addition of ISPN, ionic conductivity of the electrolyte has nearly doubled, reaching as high as 5.3 × 10−4 S cm−1. What's more, the LiFePO4 (LFP)|ISPN‐PTA|Li cell exhibits exceptional cycle stability and fast charging capabilities, maintaining stable cycling for 850 cycles at 10 C rate. Even when paired with the high‐voltage cathode, the LiNi0.6Co0.2Mn0.2O2 (NCM622)|ISPN‐PTA|Li cell achieves an impressive capacity retention of 97.59% after 165 cycles at 5 C. This study offers a novel approach for ester‐based polymer electrolytes, paving the way toward the development of stable and high‐energy Li metal battery technologies.

In Situ Analysis of Interfacial Morphological and Chemical Evolution in All‐Solid‐State Lithium‐Metal Batteries

AbstractIn situ analysis of Li plating/stripping processes and evolution of solid electrolyte interphase (SEI) are critical for optimizing all‐solid‐state Li metal batteries (ASSLMB). However, the buried solid‐solid interfaces present a challenge for detection which preclude the employment of multiple analysis techniques. Herein, by employing complementary in situ characterizations, morphological/chemical evolution, Li plating/stripping dynamics and SEI dynamics were directly detected. As a mixed ionic‐electronic conducting interface, Li|Li10GeP2S12 (LGPS) performed distinct interfacial morphological/chemical evolution and dynamics from ionic‐conducting/electronic‐isolating interface like Li|Li3PS4 (LPS), which were revealed by combination of in situ atomic force microscopy and in situ X‐ray photoelectron spectroscopy. Though Li plating speed in LGPS was higher than LPS, speed of SSE decomposition was similar and ~85 % interfacial SSE turned into SEI during plating and remained unchanged in stripping. To leverage strengths of different SSEs, an LPS‐LGPS‐LPS sandwich electrolyte was developed, demonstrating enhanced ionic conductivity and improved interfacial stability with less SSE decomposition (25 %). Using in situ Kelvin probe force microscopy, Li‐ion behavior at interface between different SSEs was effectively visualized, uncovering distribution of Li ions at LGPS|LPS interface under different potentials.

Polar groups promoting in-situ polymerization phase separation for solid electrolytes enabling solid-state lithium batteries

Plastic-crystal-embedded elastomer electrolytes (PCEEs), produced through polymerization-induced phase separation (PIPS), are gaining popularity as solid polymer electrolytes (SPEs). However, it remains to be investigated whether all monomer molecules can achieve polymerization-induced phase separation and the corresponding differences in lithium metal battery performance. Herein, we prepared PCEEs with different functional groups (OH, CN, F) through in situ polymerization. Research findings show that PCEE containing – CN or – F achieves the separation of the plastic crystalline phase and succinonitrile (SN) phase, whereas PCEE containing OH cannot due to hydrogen bonding with the SN phase. Notably, the PCEE synthesized with the F monomer (FBA-PCEE) exhibited exceptional interfacial stability with lithium metal anodes and lithium iron phosphate (LFP) cathodes, due to its unique coordination mechanism with lithium ions. The FBA-PCEE demonstrated a high ionic conductivity (2.02 × 10−3 S cm−1) and lithium-ion migration number (tLi+ = 0.75). Moreover, lithium symmetric cells incorporating FBA-PCEE demonstrated stable cycling performance for more than 1000 h at a current density of 0.1 mA cm−2, resulting in the development of a solid electrolyte interphase (SEI) rich in LiF, Li3N, and Li2CO3 over time. Additionally, incorporating FBA-PCEE facilitated the stable cycling of LPF over 1000 cycles at 0.5C, maintaining a capacity retention of 77.38 % after 500 cycles. When coupled with high-voltage Nickel Cobalt Manganese Oxide (NCM-622) cathodes and lithium metal anodes, a discharge capacity of 119.70 mAh g−1 at 0.1C was sustained after 100 cycles, exhibiting a capacity retention of 78.95 %. This study elucidates the critical role of monomer design in achieving PIPS, offering valuable insights into developing high-performance polymer composite electrolytes for advanced lithium metal batteries.

Horizontal Lithium Electrodeposition on Atomically Polarized Monolayer Hexagonal Boron Nitride.

Both uncontrolled Li dendrite growth and corrosion are major obstacles to the practical application of Li-metal batteries. Despite numerous attempts to address these challenges, effective solutions for dendrite-free reversible Li electrodeposition have remained elusive. Here, we demonstrate the horizontal Li electrodeposition on top of atomically polarized monolayer hexagonal boron nitride (hBN). Theoretical investigations revealed that the hexagonal lattice configuration and polarity of the monolayer hBN, devoid of dangling bonds, reduced the energy barrier for the surface diffusion of Li, thus facilitating reversible in-plane Li growth. Moreover, the single-atom-thick hBN deposited on a Cu current collector (monolayer hBN/Cu) facilitated the formation of an inorganic-rich, homogeneous solid electrolyte interphase layer, which enabled the uniform Li+ flux and suppressed Li corrosion. Consequently, Li-metal and anode-free full cells containing the monolayer hBN/Cu exhibited improved rate performance and cycle life. This study suggests that the monolayer hBN is a promising class of underlying seed layers to enable dendrite- and corrosion-free, horizontal Li electrodeposition for sustainable Li-metal anodes in next-generation batteries.

In Situ Electrochemical Interfacial Manipulation Enabling Lithiophilic Li Metal Anode with Inorganic‐Rich Solid Electrolyte Interphases for Stable Li Metal Batteries

Lithium‐metal anodes (LMAs) are the ultimate choice for realizing high‐energy‐density batteries; however, its use is hindered by problematic Li growth in the form of dendrites. To alleviate dendritic Li growth, the preparation of LMAs with a lithiophilic current collector (CC) is effective; however, applying a lithiophilic CC to LMAs is still challenging due to the manufacturing complexity involved in the separate lithiophilic treatment and lithiation processes. Herein, a facile one‐pot LMA fabrication method by utilizing thiourea (TU) as a precursor is proposed. A lithiophilic Cu2S layer is formed on Cu foam (CF) by the in situ electrochemical oxidation of TU (CuxSCF), and the lithiation of CC is performed via subsequent Li electrodeposition (Li@CuxSCF). The Cu2S on CuxSCF can lead to uniform Li deposition by providing lithiophilic sites, and it is converted to form ionic‐conductive Li2S‐rich solid electrolyte interphase layer. Resultantly, CuxSCF significantly enhances the cycling performance of LMAs compared to CF. Specifically, a LiFePO4/Li@CuxSCF full‐cell lithium‐metal battery (LMB) with a low n/p ratio (1.6) exhibits capacity retention of 95.6% at 0.5 C (220 cycles) and can maintain 85.0% of initial capacity (425 cycles, n/p = 4) at 2.0 C. LMBs with LiNi0.6Co0.2Mn0.2 and LiNi0.8Co0.1Mn0.1 also exhibit improved electrochemical performance.

Highly reversible Zn anode by guiding uniform Zn deposition through LiF protective layer

Deep-seated issues such as ineluctable dendrite deposition and parasitic reaction of Zn anode pose a major obstacle to the commercialization of aqueous zinc ion batteries (AZIBs). Herein, we proposed LiF as a solid-electrolyte interphase for highly reversible Zn anode. Combining experimental analyses and theoretical simulation calculations, the electronegative fluorine atoms could provide uniform zincophilic nucleation sites to regulate Zn deposition behavior. Additionally, a ZnF2 layer with outstanding Zn2+ conductive can be formed insitu thus further shielding bulk water molecules and expediting the Zn2+ transfer kinetics. Therefore, the LiF@Zn symmetric cells manifest long-cycling stability with 650 h at 1.0 mA/cm2 and 1.0 mAh/cm2 and 1000 h at 2.0 mA/cm2 and 1.0 mAh/cm2. Meanwhile, the rate performance of Zn//MnO2 and Zn//NH4V4O10 full cells are also enhanced by the LiF coating. This work provides a horizon for the design of artificial protective layer and promotes the large-scale practical development of AZIBs.

Revealing the interfacial chemistry of silicon anodes with polysiloxane electrolyte additives

Silicon (Si) anodes are promising in lithium-ion batteries owing to their high specific capacity and suitable voltage platform. However, particle volume expansion (>300 %) and the continuous consumption of Li+ to form new interfacial layers result in poor cycle performance. We report a sustainable low-cost Si material derived from photovoltaic cutting waste, showing a high initial Coulombic efficiency (86.9 %). The cycle stability of Si/graphite is enhanced in terms of a 38 % capacity retention increase in the presence of vinyl-terminated polydimethylsiloxane (Vi-PDMS) additive. The C = C bond in Vi-PDMS plays a role in reacting with hydrogen fluoride (HF) by-products to prevent the side reaction between HF and solvent. The decomposed macromolecule Si-containing Li salt serves as a part of the solid electrolyte interphase film and has low interface resistance. This formed interphase layer effectively mitigates stress concentration at the contact surface between silicon particles and the current collector caused by expansion forces.

Unlocking Fast Potassium Ion Kinetics: High-Rate and Long-Life Potassium Dual-Ion Battery for Operation at -60 °C.

Energy storage devices operating at low temperatures are plagued by sluggish kinetics, reduced capacity, and notorious dendritic growth. Herein, novel potassium dual-ion batteries (PDIBs) capable of superior performance at -60 °C, and fabricated by combining MXenes and polytriphenylamine (PTPAn) as the anode and cathode, respectively, are presented. Additionally, the reason for the anomalous kinetics of K+ (faster at low temperature than at room temperature) on the Ti3C2 anode is investigated. Theoretical calculations, crossover experiments, and in situ XRD at room and low temperatures revealed that K+ tends to bind with solvent molecules rather than anions at subzero temperatures, which not only inhibits the participation of PF6 - in the formation of the solid electrolyte interphase (SEI), but also guarantees co-intercalation behavior and suppresses undesirable K+ storage. The advantageous properties at low temperatures endow the Ti3C2 anode with fast K+ kinetics to unlock the outstanding performance of PDIB at ultralow temperatures. The PDIBs exhibit superior rate capability and high capacity retention at -40 °C and -60 °C. Impressively, after charging-discharging for 20,000 cycles at -60 °C, the PDIB retained 86.7 % of its initial capacity. This study reveals the influence of temperatures on MXenes and offers a unique design for dual-ion batteries operating at ultralow temperatures.

Unlocking Fast Potassium Ion Kinetics: High‐Rate and Long‐Life Potassium Dual‐Ion Battery for Operation at −60 °C

AbstractEnergy storage devices operating at low temperatures are plagued by sluggish kinetics, reduced capacity, and notorious dendritic growth. Herein, novel potassium dual‐ion batteries (PDIBs) capable of superior performance at −60 °C, and fabricated by combining MXenes and polytriphenylamine (PTPAn) as the anode and cathode, respectively, are presented. Additionally, the reason for the anomalous kinetics of K+ (faster at low temperature than at room temperature) on the Ti3C2 anode is investigated. Theoretical calculations, crossover experiments, and in situ XRD at room and low temperatures revealed that K+ tends to bind with solvent molecules rather than anions at subzero temperatures, which not only inhibits the participation of PF6− in the formation of the solid electrolyte interphase (SEI), but also guarantees co‐intercalation behavior and suppresses undesirable K+ storage. The advantageous properties at low temperatures endow the Ti3C2 anode with fast K+ kinetics to unlock the outstanding performance of PDIB at ultralow temperatures. The PDIBs exhibit superior rate capability and high capacity retention at −40 °C and −60 °C. Impressively, after charging‐discharging for 20,000 cycles at −60 °C, the PDIB retained 86.7 % of its initial capacity. This study reveals the influence of temperatures on MXenes and offers a unique design for dual‐ion batteries operating at ultralow temperatures.

Promoting uniform lithium deposition with Janus gel polymer electrolytes enabling stable lithium metal batteries

AbstractLithium metal batteries (LMBs) are desirable candidates owing to their high‐energy advantage for next‐generation batteries. However, the practical application of LMBs continues to be constrained by thorny safety issues with the formation and growth of Li dendrites. Herein, the ZIF‐67 MOFs are in situ coupled onto a single face of 3D porous nanofiber to fabricate an asymmetric Janus membrane, harnessing their anion adsorption capabilities to promote the uniform deposition of Li ions. In addition, the poly(ethylene glycol) diacrylate and trifluoromethyl methacrylate are introduced into nanofiber skeleton to form Janus@GPE, which preferentially reacts with Li metal to form a LiF‐rich stable SEI layer to inhibit Li dendrite growth. Importantly, the synergistic effect of the MOFs and stable solid electrolyte interphase (SEI) layer results in superior cycling performance, achieving a remarkable 2500 h cycling at 1 mA cm−2 in the Li/Janus@GPE/Li configuration. In addition, the Janus@GPE electrolyte has a certain flame retardant, which can self‐extinguish within 3 s, improving the safety performance of the batteries. Consequently, the Li/Janus@GPE/LFP flexible pouch cell exhibits favorable cycling stability (the capacity retention rate of 45 cycles is 91.8% at 0.1 C). This work provides new insights and strategies to improve the safety and practical utility of LMBs.image

Stable solvent-derived sulfur-rich inorganic solid electrolyte interphase via solvation modulation for lithium metal batteries

The utilization of lithium (Li) metal as an anode in batteries has drawn significant research interest. However, its widespread adoption has been hampered by the formation of Li dendrites and associated irreversible effects. In this study, we aim to develop a sulfur-rich inorganic solid electrolyte interphase (SEI) by incorporating Sodium 3,3′-dithiodipropane sulfonate (SPS) into a 1,3-dioxopentane/1,2-dimethoxyethane (DME/DOL) based electrolyte. The desolvation kinetics are accelerated by the unique solvation shell containing anions, as evidenced by both theoretical models and experimental data. Additionally, the combined effects of the additives lower the Li+ diffusion energy barrier significantly, promoting the deposition of compact and chunky Li, thereby facilitating the creation of an additive-derived sulfur enhanced inorganic-rich SEI. Consequently, the resultant SEI is enriched with lithium sulfide (Li2S), leading to enhanced coulombic efficiency, rate capability, and cyclic stability while reducing polarization potential. Symmetrical Li | Li cells subject to high current density and capacity (5.0 mA cm−2 and 15 mAh cm−2) demonstrate stable cycling for over 750 h. This technology demonstrates the potential to enhance the efficiency and reliability of batteries that use lithium metal anodes by reducing the formation of dendrites.

Nondisassembly Repair of Degraded LiFePO4 Cells via Lithium Restoration from the Solid Electrolyte Interphase.

The disposal of degraded batteries will be a severe challenge with the expanding market demand for lithium iron phosphate (LiFePO4 or LFP) batteries. However, due to a lack of economic and technical viability, conventional metal extraction and material regeneration are hindered from practical application. Herein, we propose a nondisassembly repair strategy for degraded cells through a lithium restoration method based on deep discharge, which can elevate the anodic potential to result in the selective oxidative decomposition and thinning of the solid electrolyte interphase (SEI) on the graphite anode. The decomposed SEI acts as a lithium source to compensate for the Li loss and eliminate Li-Fe antisite defects for degraded LFP. Through this design, the repaired pouch cells show improved kinetic characteristics, significant capacity restoration, and an extended lifespan. This proposed repair scheme relying on SEI rejuvenation is of great significance for extending the service life and promoting the secondary use of degraded cells.

In Situ Formed Gel Polymer Electrolytes Enable Stable Solid Electrolyte Interface for High-Performance Lithium Metal Batteries.

Carbonate-based electrolytes show distinct advantages in high-voltage cathodes but generate nonuniform and mechanically fragile solid-electrolyte interphase (SEI) in lithium (Li) metal batteries. Herein, we propose a LiF-rich SEI incorporating an in situ polymerized poly(hexamethylene diisocyanate)-based gel polymer electrolyte (GPE) to improve the homogeneity and mechanical stability of SEI. Fluoroethylene carbonate (FEC) as a fluorine-based additive for building LiF-rich SEI on Li metal electrodes. With this strategy, the assembled Li symmetric batteries cycled stably for 700 h, and the formation of byproducts on the Li electrode surface was significantly inhibited. The Li/LiFePO4 battery delivered significant capacity retention (91% retention after 800 cycles) at 1 C. With high-voltage LiNi0.8Co0.1Mn0.1O2 (NCM811) as cathode, the Li/GPE-FEC/NCM811 cell delivered a discharge capacity of 168.9 mAh g-1 with a capacity retention of 82% after 300 cycles at 0.5 C. From the above, the work could assist the rapid development of high-energy-density rechargeable Li metal batteries toward remarkable performance.

Unraveling the impact of pore length on the conversion reaction of Fe3O4/carbon anodes in lithium-ion batteries

Despite numerous studies investigating Fe3O4/porous carbon anode materials for high-performance lithium-ion batteries (LIBs), the inherent limitations of the Fe3O4 conversion reaction, such as low reversibility and sluggish kinetics, continue to pose significant challenges. While modifying the porous structure of Fe3O4 anodes has demonstrated considerable promise in overcoming these limitations, the precise relationship between the porous structure and Fe3O4 conversion behavior still remains unclear. Here, we explore the impact of the pore length of the anode active material on the electrochemical performance of LIBs. Using two different composites of Fe3O4 and porous carbon with varying pore lengths as model materials, we conduct various in-depth electrochemical and ex-situ analyses. Our findings confirm that a shorter pore length facilitates higher Li+ ion diffusivity compared to longer pore length. Consequently, the conversion reaction of Fe3O4 to Fe and Li2O during lithiation process can be expedited, leading to a decrease in the resistance at the solid electrolyte interphase. As a result, we demonstrate that shortening the pore length of the porous anode composite materials can enhance the initial Coulombic efficiency (CE), reversible capacity, and rate capability of LIBs.

Materials Design and Mechanistic Understanding of Tellurium and Tellurium-Sulfur Cathodes for Rechargeable Batteries.

ConspectusThe market demand for lithium-ion batteries (LIBs) has been proliferating in wide applications, from portable electronics and electric vehicles to renewable energy storage, due to their advantages of high energy density and reliable life cycles. Currently, further development of LIBs is hindered by the limited specific/volumetric capacity and high cost of conventional intercalation-type cathode materials. In this context, sulfur (S) has gained intensive attention as a conversion-type cathode because of its abundance, low cost, and high theoretical capacity (1675 mAh g-1). However, the insulating nature of S causes severe issues of sluggish redox kinetics, low S utilization, and unsatisfactory practical capacity. So far, extensive efforts have been devoted to boosting Li-S redox kinetics and enhancing cycling stability by inhibiting the shuttle effect, including developing functional electrolyte additives, introducing redox catalysts, and tailoring the S cathode structure. Partially substituting S atoms in S8 rings with high-electrical-conductivity elements (e.g., selenium, 1 × 10-3 S m-1) at the molecular level proves to be an effective strategy for tackling the above-mentioned challenges in Li-S batteries. It is noteworthy that tellurium (Te), with remarkable electrical conductivity (2 × 102 S m-1) and high density (6.24 g cm-3), is a promising battery electrode material that can realize fast electron transport and deliver volumetric capacity comparable to that of S or Se. Additionally, Te-S molecular regulation is one facile strategy to reshape Li-S chemistry, accelerate redox kinetics, and manipulate the lithiation/delithiation behaviors. Te is an effective eutectic accelerator that prevents polysulfide dissolution in Li-S batteries under the dissolution-deposition mechanism. Meanwhile, the Li-Te electrochemistry can contribute to reversible capacity in Li-TexSy batteries through Te-Li2Te conversion and enhance the materials utilization of TexSy.This Account highlights state-of-the-art advancements in applying Te or TexSy as high-capacity cathodes for rechargeable batteries. First, battery configuration and reaction pathways in Li-Te batteries are discussed, followed by the introduction of cathode design strategies to improve cathode structure stability. The limitations of this Te-only cathode are outlined in terms of the abundance, cost, and energy density. Second, the role of Te in Li-S chemistry is clarified by the analysis of the crystal structure, electrochemical behaviors, solid electrolyte interphase composition, and energy profiles. Third, recent progresses on quasi-solid-state Li-Te batteries have been introduced, focusing on flexible gel polymer electrolytes with adjustable ionic conductivity. Afterward, advancements in interface engineering by the atomic layer deposition technique in metal-Te batteries are highlighted. Additionally, mechanistic analysis in emerging zinc-TexSy batteries with outstanding areal capacity is demonstrated. Finally, we provide insightful perspectives on the future directions of material design in Te-based energy storage technologies. This Account is expected to deepen the fundamental understanding of metal-Te/TexSy chemistry and offer inspiration for the further development of Te-based high-energy-density rechargeable batteries.