The Origin of Capacity Fade in the Li2MnO3·LiMO2 (M = Li, Ni, Co, Mn) Microsphere Positive Electrode: An Operando Neutron Diffraction and Transmission X-ray Microscopy Study.

The mechanism of capacity fade of the Li2MnO3·LiMO2 (M = Li, Ni, Co, Mn) composite positive electrode within a full cell was investigated using a combination of operando neutron powder diffraction and transmission X-ray microscopy methods, enabling the phase, crystallographic, and morphological evolution of the material during electrochemical cycling to be understood. The electrode was shown to initially consist of 73(1) wt % R3̅m LiMO2 with the remaining 27(1) wt % C2/m Li2MnO3 likely existing as an intergrowth. Cracking in the Li2MnO3·LiMO2 electrode particle under operando microscopy observation was revealed to be initiated by the solid-solution reaction of the LiMO2 phase on charge to 4.55 V vs Li(+)/Li and intensified during further charge to 4.7 V vs Li(+)/Li during the concurrent two-phase reaction of the LiMO2 phase, involving the largest lattice change of any phase, and oxygen evolution from the Li2MnO3 phase. Notably, significant healing of the generated cracks in the Li2MnO3·LiMO2 electrode particle occurred during subsequent lithiation on discharge, with this rehealing being principally associated with the solid-solution reaction of the LiMO2 phase. This work reveals that while it is the reduction of lattice size of electrode phases during charge that results in cracking of the Li2MnO3·LiMO2 electrode particle, with the extent of cracking correlated to the magnitude of the size change, crack healing is possible in the reverse solid-solution reaction occurring during discharge. Importantly, it is the phase separation during the two-phase reaction of the LiMO2 phase that prevents the complete healing of the electrode particle, leading to pulverization over extended cycling. This work points to the minimization of behavior leading to phase separation, such as two-phase and oxygen evolution, as a key strategy in preventing capacity fade of the electrode.

Systematic study of Co-free LiNi0.9Mn0.07Al0.03O2 Ni-rich cathode materials to realize high-energy density Li-ion batteries.

The growing use of EVs and society's energy needs require safe, affordable, durable, and eco-friendly high-energy lithium-ion batteries (LIBs). To this end, we synthesized and investigated the removal of Co from Al-doped Ni-rich cathode materials, specifically LiNi0.9Co0.1Al0.0O2 (NCA-0), LiNi0.9Mn0.1Al0.0O2 (NMA-0), LiNi0.9Mn0.07Al0.03O2 (NMA-3), intending to enhance LIB performance and reduce the reliance on cobalt, a costly and scarce resource. Our study primarily focuses on how the removal of Co affects the material characteristics of Ni-rich cathode material and further introduces aluminum into the cathode composition to study its impacts on electrochemical properties and overall performance. Among the synthesized samples, we discovered that the NMA-3 sample, modified with 3 mol% of Al, exhibited superior battery performance, demonstrating the effectiveness of aluminum in promoting cathode stability. Furthermore, the Al-modified cathode showed promising cycle life under normal and high-temperature conditions. Our NMA-3 demonstrated remarkable capacity retention of âˆ¼ 88 % at 25 °C and âˆ¼ 81 % at 45 °C after 200 cycles at 1C, within a voltage range of 2.8-4.3 V, closely matching the performances of conventional NCM and NCA cathodes. Without cobalt, the cathodes exhibited increased cation disorder leading to inferior rate capabilities at high C-rates. In-situ transmission XRD analysis revealed that the introduction of Al has reduced the phase change and provided much-needed stability to the overall structure of the Co-free NMA-3. Altogether, the findings suggest that our aluminum-modified NMA-3 sample offers a promising approach to developing Co-free, Ni-rich cathodes, effectively paving the way toward sustainable, high-energy-density LIBs.

Two birds with one stone: One-pot concurrent Ta-doping and -coating on Ni-rich LiNi0.92Co0.04Mn0.04O2 cathode materials with fiber-type microstructure and Li+-conducting layer formation.

A novel scalable Taylor-Couette reactor (TCR) synthesis method was employed to prepare Ta-modified LiNi0.92Co0.04Mn0.04O2 (T-NCM92) with different Ta contents. Through experiments and density functional theory (DFT) calculations, the phase and microstructure of Ta-modified NCM92 were analyzed, showing that Ta provides a bifunctional (doping and coating at one time) effect on LiNi0.92Co0.04Mn0.04O2 cathode material through a one-step synthesis process via a controlling suitable amount of Ta and Li-salt. Ta doping allows the tailoring of the microstructure, orientation, and morphology of the primary NCM92 particles, resulting in a needle-like shape with fine structures that considerably enhance Li+ ion diffusion and electrochemical charge/discharge stability. The Ta-based surface-coating layer effectively prevented microcrack formation and inhibited electrolyte decomposition and surface-side reactions during cycling, thereby significantly improving the electrochemical performance and long-term cycling stability of NCM92 cathodes. Our as-prepared NCM92 modified with 0.2 mol% Ta (i.e., T2-NCM92) exhibits outstanding cyclability, retaining 84.5 % capacity at 4.3 V, 78.3 % at 4.5 V, and 67.6 % at 45 â„ƒ after 200 cycles at 1C. Even under high-rate conditions (10C), T2-NCM92 demonstrated a remarkable capacity retention of 66.9 % after 100 cycles, with an initial discharge capacity of 157.6 mAh g-1. Thus, the Ta modification of Ni-rich NCM92 materials is a promising option for optimizing NCM cathode materials and enabling their use in real-world electric vehicle (EV) applications.

Boosting the Interfacial Stability of the Li6PS5Cl Electrolyte with a Li Anode via In Situ Formation of a LiF-Rich SEI Layer and a Ductile Sulfide Composite Solid Electrolyte.

Due to its good mechanical properties and high ionic conductivity, the sulfide-type solid electrolyte (SE) can potentially realize all-solid-state batteries (ASSBs). Nevertheless, challenges, including limited electrochemical stability, insufficient solid-solid contact with the electrode, and reactivity with lithium, must be addressed. These challenges contribute to dendrite growth and electrolyte reduction. Herein, a straightforward and solvent-free method was devised to generate a robust artificial interphase between lithium metal and a SE. It is achieved through the incorporation of a composite electrolyte composed of Li6PS5Cl (LPSC), polyethylene glycol (PEG), and lithium bis(fluorosulfonyl)imide (LiFSI), resulting in the in situ creation of a LiF-rich interfacial layer. This interphase effectively mitigates electrolyte reduction and promotes lithium-ion diffusion. Interestingly, including PEG as an additive increases mechanical strength by enhancing adhesion between sulfide particles and improves the physical contact between the LPSC SE and the lithium anode by enhancing the ductility of the LPSC SE. Moreover, it acts as a protective barrier, preventing direct contact between the SE and the Li anode, thereby inhibiting electrolyte decomposition and reducing the electronic conductivity of the composite SE, thus mitigating the dendrite growth. The Li|Li symmetric cells demonstrated remarkable cycling stability, maintaining consistent performance for over 3000 h at a current density of 0.1 mA cm-2, and the critical current density of the composite solid electrolyte (CSE) reaches 4.75 mA cm-2. Moreover, the all-solid-state lithium metal battery (ASSLMB) cell with the CSEs exhibits remarkable cycling stability and rate performance. This study highlights the synergistic combination of the in-situ-generated artificial SE interphase layer and CSEs, enabling high-performance ASSLMBs.

Mechanistic Study on Artificial Stabilization of Lithium Metal Anode via Thermal Pyrolysis of Ammonium Fluoride in Lithium Metal Batteries.

The use of the "Holy Grail" lithium metal anode is pivotal to achieve superior energy density. However, the practice of a lithium metal anode faces practical challenges due to the thermodynamic instability of lithium metal and dendrite growth. Herein, an artificial stabilization of lithium metal was carried out via the thermal pyrolysis of the NH4F salt, which generates HF(g) and NH3(g). An exposure of lithium metal to the generated gas induces a spontaneous reaction that forms multiple solid electrolyte interface (SEI) components, such as LiF, Li3N, Li2NH, LiNH2, and LiH, from a single salt. The artificially multilayered protection on lithium metal (AF-Li) sustains stable lithium stripping/plating. It suppresses the Li dendrite under the Li||Li symmetric cell. The half-cell Li||Cu and Li||MCMB systems depicted the attributions of the protective layer. We demonstrate that the desirable protective layer in AF-Li exhibited remarkable capacity retention (CR) results. LiFePO4 (LFP) showed a CR of 90.6% at 0.5 mA cm-2 after 280 cycles, and LiNi0.5Mn0.3Co0.2O2 (NCM523) showed 58.7% at 3 mA cm-2 after 410 cycles. Formulating the multilayered protection, with the simultaneous formation of multiple SEI components in a facile and cost-effective approach from NH4F as a single salt, made the system competent.

Preparation of long-term cycling stable ni-rich concentration-gradient NCMA cathode materials for li-ion batteries.

Nickel-rich (Ni > 90 %) cathodes are regarded as one of the most attractive because of their high energy density, despite their poor stability and cycle life. To improve their performance, in this study we synthesized a double concentration-gradient layered Li[Ni0.90Co0.04Mn0.03Al0.03]O2 oxide (CG-NCMA) using a continuous co-precipitation Taylor-Couette cylindrical reactor (TCCR) with a Ni-rich-core, an Mn-rich surface, and Al on top. The concentration-gradient morphology was confirmed through cross-sectional EDX line scanning. The as-synthesized sample exhibited excellent electrochemical performance at high rates (5C/10C), as well as cyclability (91.5 % after 100 cycles and 70.3 % after 500 cycles at 1C), superior to that (83.4 % and 47.6 %) of its non-concentration-gradient counterpart (UC-NCMA). The Mn-rich surface and presence of Al helped the material stay structurally robust, even after 500 cycles, while also suppressing side reactions between the electrode and electrolyte, resulting in better overall electrochemical performance. These enhancements in performance were studied using TEM, SEM, in-situ-XRD, XPS, CV, EIS and post-mortem analyses. This synthetic method enables the highly scalable production of CG-NCMA samples with two concentration-gradient structures for practical applications in Li-ion batteries.

The Entanglement of Li Capping and Deposition: An Operando Optical Microscopy Study.

Dendrite growth and low Coulombic efficiency impede the practical application of Li-metal batteries. As such, monitoring Li deposition and stripping in real-time is crucial to understanding the fundamental lithium growth kinetics. This work presents an operando optical microscopic technique that enables precise current density control and quantification of Li layer properties (i.e., thickness and porosity) to study Li growth in various electrolytes. We discover the robustness and porosity of the remaining capping layer after the Li stripping process as the critical features governing the subsequent dendrite propagation behavior, resulting in distinct capping and stacking phenomena that affect Li growth upon cycling. While dendrite propagation quickly occurs through the fracture of the fragile Li capping layer, uniform Li plating/stripping can be facilitated by the compact and robust capping layer even at high current densities. This technique can be extended to evaluate dendrite suppression treatments in various metal batteries, providing in-depth information on metal growth mechanisms.

Lewis Acid Probe for Basicity of Sulfide Electrolytes Investigated by 11B Solid-State NMR.

Sulfide-based solid-state lithium-ion batteries (SSLIB) have attracted a lot of interest globally in the past few years for their high safety and high energy density over the traditional lithium-ion batteries. However, sulfide electrolytes (SEs) are moisture-sensitive which pose significant challenges in the material preparation and cell manufacturing. To the best of our knowledge, there is no tool available to probe the types and the strength of the basic sites in sulfide electrolytes, which is crucial for understanding the moisture stability of sulfide electrolytes. Herein, we propose a new spectral probe with the Lewis base indicator BBr3 to probe the strength of Lewis basic sites on various sulfide electrolytes by 11B solid-state NMR spectroscopy (11B-NMR). The active sulfur sites and the corresponding strength of the sulfide electrolytes are successfully evaluated by the proposed Lewis base probe. The probed strength of the active sulfur sites of a sulfide electrolyte is consistent with the results of DFT (density functional theory) calculation and correlated with the H2S generation rate when the electrolyte was exposed in moisture atmosphere. This work paves a new way to investigate the basicity and moisture stability of the sulfide electrolytes.

Lithium Nafion-Modified Li6.05Ga0.25La3Zr2O11.8F0.2 Trilayer Hybrid Solid Electrolyte for High-Voltage Cathodes in All-Solid-State Lithium-Metal Batteries.

All-solid-state batteries containing ceramic-polymer solid electrolytes are possible alternatives to lithium-metal batteries containing liquid electrolytes in terms of their safety, energy storage, and stability at elevated temperatures. In this study we prepared a garnet-type Li6.05Ga0.25La3Zr2O11.8F0.2 (LGLZOF) solid electrolyte modified with lithium Nafion (LiNf) and incorporated it into poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) matrixes. We used a solution-casting method to obtain bilayer (Bi-HSE) and trilayer (Tri-HSE) hybrid solid electrolytes. A layer of functionalized multiwalled carbon nanotubes (f-MWCNTs) coated with LiNf (LiNf@f-MWCNT) in the Tri-HSE led to good compatibility with the polymer slurry and adhered well to the Li anode, thereby improving the interfacial contact at the electrode-solid electrolyte interface and suppressing dendrite growth. The Tri-HSE membrane displayed high ionic conductivity (5.6 × 10-4 S cm-1 at 30 °C), a superior Li+ transference number (0.87), and a wide electrochemical window (0-5.0 V vs Li/Li+). In addition, Li symmetrical cells incorporating this hybrid electrolyte possessed excellent interfacial stability over 600 h at 0.1 mA cm-2 and a high critical current density (1.5 mA cm-2). Solid-state lithium batteries having the structure LiNf@LiNi0.8Co0.1Mn0.1O2/Tri-HSE/Li delivered excellent room-temperature stable cycling performance at 0.5C, with a capacity retention of 85.1% after 450 cycles.

Highly Concentrated Salt Electrolyte for a Highly Stable Aqueous Dual-Ion Zinc Battery.

A zinc metal anode for zinc-ion batteries is a promising alternative to solve safety and cost issues in lithium-ion batteries. The Zn metal is characterized by its high theoretical capacity (820 mAh g-1), low redox potential (0.762 V vs SHE), low toxicity, high abundance on Earth, and high stability in water. Taking advantage of the stability of Zn in water, an aqueous Zn ion battery with low cost, high safety, and easy-to-handle features can be developed. To minimize water-related parasitic reactions, this work utilizes a highly concentrated salt electrolyte (HCE) with dual salts─1 m Zn(OTf)2 + 20 m LiTFSI. MD simulations prove that Zn2+ is preferentially coordinated with O in the TFSI- anion from HCE instead of O in H2O. HCE has a broadened electrochemical stability window due to suppressed H2 and O2 evolution. Some advanced ex situ and in situ/in operando analysis techniques have been applied to evaluate the morphological structure and the composition of the in situ formed passivation layer. A dual-ion full Zn||LiMn2O4 cell employing HCE has an excellent capacity retention of 92% after 300 cycles with an average Coulombic efficiency of 99.62%. Meanwhile, the low concentration electrolyte (LCE) cell degrades rapidly and is short-circuited after 66 cycles with an average Coulombic efficiency of 96.91%. The battery's excellent cycling performance with HCE is attributed to the formation of a stable anion-derived solid-electrolyte interphase (SEI) layer. On the contrary, the high free water activity in LCE leads to a water-derived interfacial layer with unavoidable dendrite growth during cycling.

Lithium Oxalate as a Lifespan Extender for Anode-Free Lithium Metal Batteries.

Anode-free lithium metal batteries (AFLMBs) have been extensively studied due to their intrinsic high energy and safety without a metallic Li anode in cell design. Yet, the dendrite and dead-Li buildup continuously consumes the active Li upon cycling, leading to the poor lifespan of AFLMBs. Here, we introduce lithium oxalate into the cathode as an electrode additive providing a Li reservoir to extend the lifespan of AFLMBs. The AFLMB using 20% lithium oxalate and a LiNi0.3Co0.3Mn0.3O2 composite cathode exhibits >80 and 40% capacity retention after 50 and 100 cycles, respectively, outperforming the poor cycle life of fewer than 20 cycles obtained from the cell using a pure LiNi0.3Co0.3Mn0.3O2 cathode. Surprisingly, the average Coulombic efficiency of AFLMBs is found to improve as the amount of lithium oxalate increases in the composite cathode. This abnormal phenomenon could be attributed to the as-formed carbon dioxide after the first activation cycle forming a Li2CO3-rich solid-electrolyte interphase and improving the Li deposition and stripping efficiency. The findings in this work provide a new strategy to delay the capacity roll-over of AFLMBs from an electrode engineering perspective, which can be coupled with other approaches such as functional electrolytes synergistically to further improve the cycle life of AFLMBs for practical application.

Electrochemical Characteristics of a Polymer/Garnet Trilayer Composite Electrolyte for Solid-State Lithium-Metal Batteries.

Although solid-state Li-metal batteries (LMBs) featuring polymer-based solid electrolytes might one day replace conventional Li-ion batteries, the poor Li-ion conductivity of solid polymer electrolytes at low temperatures has hindered their practical applications. Herein, we describe the first example of using a co-precipitation method in a Taylor flow reactor to produce the metal hydroxides of both the Ga/F dual-doped Li7La3Zr2O12 (Ga/F-LLZO) ceramic electrolyte precursors and the Li2MoO4-modified Ni0.8Co0.1Mn0.1O2 (LMO@T-LNCM 811) cathode materials for LMBs. The Li/Nafion (LiNf)-coated Ga/F-LLZO (LiNf@Ga/F-LLZO) ceramic filler was finely dispersed in the poly(vinylidene fluoride)/polyacrylonitrile/lithium bis(trifluoromethanesulfonimide)/succinonitrile matrix to give a trilayer composite polymer electrolyte (denoted "Tri-CPE") through a simple solution-casting. The bulk ionic conductivity of the Tri-CPE at room temperature was approximately 4.50 × 10-4 S cm-1 and exhibited a high Li+ ion transference number (0.84). It also exhibits a broader electrochemical window of 1-5.04 V versus Li/Li+. A full cell based on a CR2032 coin cell containing the LMO@T-LNCM811-based composite cathode, when cycled under 1 C/1 C at room temperature for 300 cycles, achieved an average Columbic efficiency of 99.4% and a capacity retention of 89.8%. This novel fabrication strategy for Tri-CPE structures has potential applications in the preparation of highly safe high-voltage cathodes for solid-state LMBs.

Decoupling the origins of irreversible coulombic efficiency in anode-free lithium metal batteries.

Anode-free lithium metal batteries are the most promising candidate to outperform lithium metal batteries due to higher energy density and reduced safety hazards with the absence of metallic lithium anode during initial cell fabrication. In general, researchers report capacity retention, reversible capacity, or rate capability of the cells to study the electrochemical performance of anode-free lithium metal batteries. However, evaluating the behavior of batteries from limited aspects may easily overlook other information hidden deep inside the meretricious results or even lead to misguided data interpretation. In this work, we present an integrated protocol combining different types of cell configuration to determine various sources of irreversible coulombic efficiency in anode-free lithium metal cells. The decrypted information from the protocol provides an insightful understanding of the behaviors of LMBs and AFLMBs, which promotes their development for practical applications.

Dual-Doped Cubic Garnet Solid Electrolytes with Superior Air Stability.

Li7La3Zr2O12 (LLZO) garnet is one kind of solid electrolyte drawing extensive attention due to its good ionic conductivity, safety, and stability toward lithium metal anodes. However, the stability problem during synthesis and storage results in high interfacial resistance and prevents it from practical applications. We synthesized air-stable dual-doped Li6.05La3Ga0.3Zr1.95Nb0.05O12 ((Ga, Nb)-LLZO) cubic-phase garnets with ionic conductivity of 9.28 × 10-3 S cm-1. The impurity-phase species formation on the garnet pellets after air exposure was investigated. LiOH and Li2CO3 can be observed on the garnet pellets by Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) once the garnets are exposed to humid air or come in contact with water. The (Ga, Nb)-LLZO garnet is found to form less LiOH and Li2CO3, which can be further reduced or removed after drying treatment. To confirm the stability of the garnet, an electrochemical test of the Li//Li symmetric cell was also performed in comparison with previously reported garnets (Li7La2.75Ca0.25Zr1.75Nb0.25O12, (Ca, Nb)-LLZO). The dual-doped (Ga, Nb)-LLZO showed less polarized and stable plating/stripping behavior than (Ca, Nb)-LLZO. Through Rietveld refinement of XRD patterns of prepared materials, dopant Ga was found to preferably occupy the Li site and Nb takes the Zr site, while dopant Ca mainly substituted La in the reference sample. The inherited properties of the dopants in (Ga, Nb)-LLZO and their structural synergy explain the greatly improved air stability and reduced interfacial resistance. This may open a new direction to realize garnet-based solid electrolytes with lower interfacial resistance and superior air stability.