High-voltage Cathode Materials Research Articles

Microstructural Insights into Performance Loss of High-Voltage Spinel Cathodes for Lithium-ion Batteries.

Spinel-structured LiNix Mn2-x O4 (LNMO), with low-cost earth-abundant constituents, is a promising high-voltage cathode material for lithium-ion batteries. Even though extensive electrochemical investigations have been conducted on these materials, few studies have explored correlations between their loss in performance and associated changes in microstructure. Here, down to the atomic scale, the structural evolution of these materials is investigated upon the progressive cycling of lithium-ion cells. Transgranular cracking is revealed to be a key feature during cycling; this cracking is initiated at the particle surface and leads to the penetration of electrolytes along the crack path, thereby increasing particle exposure to the electrolyte. The lattice structure on the crack surface shows spatial variances, featuring a top layer of rock-salt, a sublayer of a Mn3 O4 -like arrangement, and then a mixed-cation region adjacent to the bulk lattice. The transgranular cracking, along with the emergence of local lattice distortion, becomes more evident with extended cycling. Further, phase transformation at primary particle surfaces and void formation through vacancy condensation is found in the cycled samples. All these features collectively contribute to the performance degradation of the battery cells during electrochemical cycling.

K2VOP2O7 as a novel high-voltage cathode material for potassium ion batteries

V-based polyanionic electrode materials are attractive in rechargeable batteries for their abundant redox centers, high working voltage and good structural stability. Here we report for the first time the synthesis and application of a novel V-based polyanionic compound K2VOP2O7 as a potential potassium storage material. It is prepared at a relatively low temperature of 550 °C using a conventional solid-state route, followed by sanding or ball milling to reduce the particle size. The material belongs to a tetragonal structure with an open framework, which provides pathways for K+ diffusion. The sanded and ball-milled samples can deliver a specific discharge capacity of 83 and 89 mAh g−1, respectively, both of which are close to the theoretical value of 84 mAh g−1, involving the one-electron-transfer redox of V5+/V4+. The sanded sample runs at a median discharge potential of 3.6 V (vs. K+/K). Combining the merits of facile synthesis and good electrochemical properties, K2VOP2O7 is recognized by this study as a new member of the pyrophosphate cathode family for potassium ion batteries.

K3 v2 (Po4 )3 /C as a New High-Voltage Cathode Material for Calcium-Ion Batteries with a Water-In-Salt Electrolyte.

Aqueous Ca-ion batteries (ACIBs) attract immense attention due to its high safety and the high abundance of calcium. However, the development of ACIBs is hindered by the lack of high voltage cathode materials to host the large radius and divalent Ca2+ . Herein, polyanionic phosphate K3 V2 (PO4 )3 /C (KVP/C) is provided as a new cathode material for ACIBs. Due to the robust structure of polyanion material and the wide electrochemical window of water-in-salt electrolyte, KVP/C delivers a high working voltage of 3.74V versus Ca2+ /Ca with a specific capacity of 102.4mAh g-1 and a long-life of 6000 cycles at 500mA g-1 . Furthermore, the calcium storage mechanism of KVP/C is shown to be the coexistence of solid solution and two-phase reaction by in situ X-ray diffraction, ex situ transmission electron microscope, and X-ray photoelectron spectroscopy. Finally, an aqueous calcium-ion full cell, based on an organic compound as anode and KVP/C as cathode, is constructed and it shows good stability for 200 cycles and a specific capacity of 80.2mAh g-1 . This work demonstrates that vanadium-based phosphate materials are promising high-voltage cathode materials for ACIBs and renew the prospects for ACIBs.

Novel layered iron vanadate as a stable high-voltage cathode material for nonaqueous magnesium-ion batteries

Novel layered iron vanadate as a stable high-voltage cathode material for nonaqueous magnesium-ion batteries

In Situ Forming Gel Polymer Electrolyte for High Energy-Density Lithium Metal Batteries.

In situ forming gel polymer electrolyte (GPE) is one of the most feasible ways to improve the safety and cycle performances of lithium metal batteries with high energy density. However, most of the in situ formed GPEs are not compatible with high-voltage cathode materials. Here, this work provides a novel strategy to in situ form GPE based on the mechanism of Ritter reaction. The Ritter reaction in liquid electrolyte has the advantage of appropriate reaction temperature and no additional additives. The polymer chains are cross-linked by amide groups with the formation of GPE with superior electrochemical properties. The GPE has high ionic conductivity (1.84 mS cm-1 ), wide electrochemical stability window (>5.25V) and high lithium ion transference number (≈0.78), compatible with high-voltage cathode materials. The Li|LiNi0.6 Co0.2 Mn0.2 O2 batteries with in situ formed GPE show excellent long-term cycle stability (93.4%, 300 cycles). The density functional theory calculation and X-ray photoelectron spectroscopyresults verify that the amide and nitrile groups are beneficial for stabilizing cathode structure and promoting uniform Li deposition on Li anode. Furthermore, the in situ formed GPE exhibits excellent electrochemical performance in Graphite|LiMn2 O4 and Graphite|LiNi0.5 Co0.2 Mn0.3 O2 pouch batteries. This approach is adaptable to current battery technologies, which will be sure to promote the development of high energy-density lithium-ion batteries.

Active Learning Platform for Accelerating the Search for High-Voltage Cathode Materials in an Extensive Chemical Space

Active Learning Platform for Accelerating the Search for High-Voltage Cathode Materials in an Extensive Chemical Space

Aligned carbon fibers-carbon nanotube-polymer-based composite as lithium-ion battery current collector

High energy density demand is pushing the development of high-voltage cathode materials, which necessitates improved electrochemical stability of other battery components such as binders, electrolytes, and current collectors. Current collectors are considered to be an inactive component but still play an essential role. In this study, a metal-free composite film containing directionally aligned carbon fiber (CF), carbon nanotube (CNT), and polymer (P) was developed to replace aluminum foil as a cathode current collector, which relies on forming an Al2O3 layer to ensure electrochemical stability at high voltage. Each component in the new cathode current collector played a functional role. The CNTs provided uniform current densities, and CFs improved the electronic conductivity and mechanical strength of the composite material. The polymer enhanced the adhesion of the cathode coating with the current collector and provided an impervious support to the cathode materials. The CF-CNT-P composite demonstrated excellent electrochemical and thermal stability. Cathodes coated on the CF-CNT-P composite exhibited lower charge transfer resistance, improved rate capability, and improved cyclic stability compared with the cathodes deposited on conventional aluminum foil. Additionally, the composite current collector was lighter (1.81 mg/cm2 and 15 µm thick) than the commonly used aluminum foil (4.35 mg/cm2 and 15 µm thick), which can increase the cell energy density. Additionally, the CF-CNT-P did not need to be separated from the cathode coating during recycling and can be burnt out with binder, simplifying the recycling process.

Enhancing the Electrochemical Properties of the Layered-Type K0.4V2O5 Cathode Materials through Cationic Metal Substitution in K Sites

Layered-type K0.4V2O5 have been widely investigated as cathode materials for potassium-ion batteries (PIBs) due to their high specific capacity. [1,2] However, sluggish intercalation kinetics of K ions into their crystal structure generally result in drastic capacity fading and poor power capability. [3] Here, we present significantly enhanced K-ion storage performances of the layered-type K0.4V2O5 cathode enabled by substitution of cationic metal for K-site. Density functional theory calculations data indicates that cationic metal prefer to occupy the K-site than transition metal layer. During charge and discharge process, inactive cationic metal acts as a pillar, thereby suppressing the irreversible phase transition and structural deterioration. In addition, cationic metal creates vacancies at k site, improving K-ion diffusion kinetics. Compared to K0.4V2O5, the modified cathode demonstrated the better cycling stability and power capability. A insitu X-ray diffraction and X-ray absorption near edge structure was used to verify role of cationic metal in improving electrochemical performance of the K0.4V2O5 cathode. Deng, X. Niu, G. Ma, Z. Yang, L. Zeng, Y. Zhu, L. Guo. Layered Potassium Vanadate K0.5V2O5 as a Cathode Material for Nonaqueous Potassium Ion Batteries, Adv. Func. Mater. 28 (2018) 1800670.Yang, Z. Liu, L. Deng, L. Tan, X. Niu, M. M. S. Sanad, L. Zeng, Y. Zhu. A Non-Topotactic Redox Reaction enabled K2V3O8 as a High Voltage Cathode Material for Potassium-Ion Batteries, Chem. Commun. 55 (2019) 14988–14991.Q. Fu, A. Sarapulove, L. Zhu, G. Melinte, A. Missyul, E. Welter, X. Luo, M. Knapp, H. Ehrenberg, S. Dsoke. In Operando Study of Orthorhombic V2O5 as Positive Electrode Materials for K-Ion Batteries, J. Energy Chem. 62 (2021) 627–636.

Rationalizing Na-ion solvation structure by weakening carbonate solvent coordination ability for high-voltage sodium metal batteries

Commercial carbonate-based electrolytes feature highly reactive activities with alkali metals, yielding low Coulombic efficiencies and poor cycle life in lithium metal batteries, which possess much higher chemical activity in the rising star sodium metal batteries. To be motivated, we have proposed that decreasing the solvent solvation ability in carbonate-based electrolytes stepwise could enable long-term stable cycling of high-voltage sodium metal batteries. As the solvation capacity reduces, more anions are enticed into the solvation sheath of Na+, resulting in the formation of the more desirable interphase layers on the surface of the anode and the cathode. The inorganic-dominated interphases allow highly efficient Na+ deposition/stripping processes with a lower rate of dead sodium generation, as well as maintain a stable structure of the high-voltage cathode material. Specifically, the assembled Na||Na3V2(PO4)2F3 battery exhibits an accelerated ion diffusion kinetics and achieves a higher capacity retention of 85.9% with during the consecutive 200 cycles under the high voltage of 4.5 V. It is anticipated that the tactics we have proposed could be applicable in other secondary metal battery systems as well.

Prospective Application, Mechanism, and Deficiency of Lithium Bis(oxalate)Borate as the Electrolyte Additive for Lithium‐Batteries

AbstractLithium bis(oxalate)borate (LiBOB) is one of the most common film‐forming electrolyte additives used in lithium ion batteries (LIBs), since it can form a dense boron‐containing polymer as a solid electrolyte interlayer (or cathode electrolyte interlayer) in order to isolate the electrode material from the electrolyte and prevent side reactions. LiBOB can serve as HF scavenger to maintain the structural integrity of electrodes via avoiding the transition metal dissolution caused by HF attack. LiBOB also can react with LiPF6 to generate lithium difluoro (oxalate)borate (LiDFOB) that can be further used as a clean‐up agent for reactive oxygen radicals. This article lists the application of LiBOB in high capacity and high voltage cathode materials, and also reviews the working mechanisms of LiBOB used in these materials to improve the performance of LIBs. Finally, it presents the current shortcomings of LiBOB and strategies to overcome these. This article is expected to provide useful insights for employing LiBOB as a feasible method of dealing with the difficulty of running high capacity LIBs stably under high voltage.

Recent Advances and Perspectives on the Promising High-Voltage Cathode Material of Na3 (VO)2 (PO4 )2 F.

Na3 (VO)2 (PO4 )2 F (NVOPF) has emerged as one of the most promising cathode materials for sodium-ion batteries (SIBs) attributed to its high specific capacity (130 mAh g-1 ), high operation voltage (>3.9V vs Na+ /Na), and excellent structural stability (<2% volume change). However, the comparatively low intrinsic electronic conductivity (≈10-7 S cm-1 ) of NVOPF leads to unsatisfactory electrochemical performance, especially at high rates, limiting its practical applications. To improve the conductivity and enhance Na storage performance, many efforts have been devoted to designing NVOPF, including morphology optimization, hybridization with conductive materials, metal-ion doping, Na-site regulation, and F/O ratio adjustment. These attempts have shown some encouraging achievements and shed light on the practical application of NVOPF cathodes. This work aims to provide a general introduction, synthetic methods, and rational design of NVOPF to give a deeper understanding of the recent progress. Additionally, the unique microstructure of NVOPF and its relationship with Na storage properties are also described in detail. The current status, as well as the advances and limitations of such SIB cathode material, are reported. Finally, future perspectives and guidance for advancing high-performance NVOPF cathodes toward practical applications are presented.

Ultrathin PEO based electrolyte for high voltage lithium metal batteries enabled by polymer host-plasticizer interactions

Poly(ethylene oxide) (PEO) stands out in solid-state Li metal batteries (SSLMBs) for its high viability, low expanse and superior compatibility with Li anode, but its insufficient ionic conductivity at ambient temperature and limited electrochemical stability windows make it difficult to work at ambient temperature and pair with high voltage cathode materials. Herein, an ultrathin dual-solvent PEO based polymer electrolyte (DSPE) with 22 μm is proposed to tackle these issues. The introduction of tetraethylene glycol dimethyl ether (TEGDME) and succinonitrile (SN) as plasticizers friendly to Li anode and NCM622, respectively, not only greatly improves the conductivity of PEO at room temperature, but also significantly enhances the compatibility of electrolyte-electrode interface. More importantly, the PEO polymer host-solvent interactions successfully anchor the free solvent small molecules of TEGDME and SN around PEO host to avoid their damage to the electrolyte-electrode interface. Improved NCM622|DSPE|Li battery provides prominent cycle life with a capacity retention of 80.0 % after 300 cycles at 0.1C at 30 °C. The application of PEO based polymer electrolyte in SSLMBs is successfully realized by taking advantage of polymer host-plasticizer interactions.

Bifunctional urea surface-modified high voltage LiNi0.5Mn1.5O4 cathode for enhanced electrochemical performance

Spinel LiNi0.5Mn1.5O4 (LNMO) cathode material has high specific energy density due to its high working voltage (4.7 V vs. Li/Li+). However, high voltage inevitably brings instability of the surface and interface layer properties and ultimately electrolyte decomposition and irreversible side reactions, which incurs structural degradation, capacity decline, and poor kinetics. Herein, a simple and novel surface modification strategy is proposed to obtain a bifunctional modification cathode material with carbon–nitrogen nanocoating and surface disorder phase transition, which is prepared through gas–solid heat treatment of pristine material and urea in a closed reactor. The surface disordered phase transition introduces favorable oxygen vacancies and synchronously constructs the fast diffusion channel of lithium ions, while the carbon–nitrogen nanocoating effectively alleviates the impedance growth of the electrode/electrolyte interface. Therefore, the surface modified U-LMNO exhibits an initial discharge capacity of 130.1 mAh g−1 at 0.2 C and a capacity retention rate of 95.1% after 200 cycles at 1 C, significantly superior to pristine P-LMNO. These results highlight the essentiality of high-voltage LNMO cathode material surface interface design and facilitate the development and commercialization of high-energy-density LNMO-based lithium-ion batteries.

Synthesis of high-voltage cathode material using the Taylor-Couette flow-based co-precipitation method.

LiNi0.5Mn1.5O4 (LNMO), a next-generation high-voltage battery material, is promising for high-energy-density and power-density lithium-ion secondary batteries. However, rapid capacity degradation occurs due to problems such as the elution of transition metals and the generation of structural distortion during cycling. Herein, a new LNMO material was synthesized using the Taylor-Couette flow-based co-precipitation method. The synthesized LNMO material consisted of secondary particles composed of primary particles with an octahedral structure and a high specific surface area. In addition, the LNMO cathode material showed less structural distortion and cation mixing as well as a high cyclability and rate performance compared with commercially available materials.

Low-Concentration Electrolyte Enables High-Voltage Positive Electrode Na4Co3(PO4)2P2O7 with Good Cycle Stability

Low energy density has been a limiting factor for further large-scale commercialization of sodium-ion batteries (SIBs). In this work, we prepare a high-voltage cathode material Na4Co3(PO4)2P2O7 with a low carbon content by a simple solid-state method. In order to counter the poor oxidative stability of the conventional electrolyte, the highly fluorinated co-solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) is introduced to adjust the Na+ solvation sheath structure. Consequently, we design a low-concentration SIB electrolyte (0.3 M NaPF6 in PC/FEC/TTE = 1/1/4, v/v/v). The oxidation stability of this electrolyte is greatly improved due to the special Na+ solvation sheath structure. Under high-voltage cycling, it can form a dense and thin cathode electrolyte interphase film on the cathode surface, which improves the interfacial stability between the electrolyte and the cathode material. Thus, the Na||NCPP cells in the 0.3 M-114 electrolytes maintain good cycle stability even when charged to a high voltage of 4.7 V. Meanwhile, it achieves a reversible capacity of 95.7 mA h g–1 in the initial cycle and a capacity retention of 94.25% after 150 cycles at 1 C. Moreover, it has an energy density of up to 420 W h kg–1 at 1 C. This study provides a practical way to establish a stable interface between the high-voltage positive electrode and the electrolyte in SIBs.

Tragacanth, an Exudate Gum as Suitable Aqueous Binder for High Voltage Cathode Material

The improvements in future-generation lithium-ion batteries cannot be exclusively focused on the performance. Other aspects, such as costs, processes, and environmental sustainability, must be considered. Research and development of new active materials allow some fundamental aspects of the batteries to be increased, such as power and energy density. However, one of the main future challenges is the improvement of the batteries’ electrochemical performance by using “non-active” materials (binder, current collector, separators) with a lower cost, lower environmental impact, and easier recycling procedure. Focusing on the binder, the main goal is to replace the current fluorinated compounds with water-soluble materials. Starting from these considerations, in this study we evaluate, for the first time, tragacanth gum (TG) as a suitable aqueous binder for the manufacturing process of a cobalt-free, high-voltage lithium nickel manganese oxide (LNMO) cathode. TG-based LNMO cathodes with a low binder content (3 wt%) exhibited good thermal and mechanical properties, showing remarkably high cycling stability with 60% capacity retention after more than 500 cycles at 1 C and an outstanding rate capability of 72 mAh g−1 at 15 C. In addition to the excellent electrochemical features, tragacanth gum also showed excellent recycling and recovery properties, making this polysaccharide a suitable and sustainable binder for next-generation lithium-ion batteries.

A dual-halogen electrolyte for protective-layer-free all-solid-state lithium batteries

Halide-type solid electrolytes (SEs) have emerged as a new class of promising Li+ conductors due to their high ionic conductivity, good deformability and excellent oxidation stability. Nevertheless, to move a step closer to the application in all-solid-state lithium batteries (ASSLBs), the poor compatibility against metal anode for halide SEs needs to be addressed. Herein, a dual-halogen trigonal SE, Li2ZrCl6-xFx is developed. With the proper incorporation of F, the SE can maintain high ionic conductivity and considerable moisture stability. Moreover, protective-layer-free ASSLBs prepared from the single SE and high-voltage cathode materials LiCoO2 can be reversibly cycled in the voltage window of 2.52–4.32 V (versus Li+/Li) with a high initial coulombic efficiency of 95.57%, and maintain 76% of the initial capacity after 70 cycles. The good electrochemical performance is originated from the in-situ formed interface protective layer between SE and Li alloy, as demonstrated by X-ray photoelectron spectroscopy and computational characterizations. This work indicates that developing mixed halogen-based SEs is a cost-effective way to improve the stability of halide SEs against alkali metal anode, and could accelerate the application for high-voltage ASSLBs.

Reevaluating the stability of the PEO-based solid-state electrolytes for high voltage solid-state batteries

This work shows how PEO-based solid state-electrolyte materials can be more stable than commonly expected when used with some types of high voltage cathode materials. Potentiodynamic and galvanostatic tests were performed in test cells using PEO electrolyte layers with either LiNixMnyCozO2 or LiCoO2 cathode materials. We found that the high voltage instability of PEO-based solid-state cells is profoundly affected by the interfacial instability of the cathode material used Specifically, the in the presence of PEO electrolyte, LiCoO2 electrodes were observed to undergo an irreversible oxidation process where they eventually shattered into small pieces, thus leading to a rapid irreversible loss in capacity. In contrast, we found that the PEO-based solid-state electrolytes could be stably cycled with high-nickel content cathode materials (NCM 811, 532, and 111) stably at a cell potential up to 4.5 V vs. Li/Li+ over many cycles with minimal capacity deterioration; this unexpected degree of stability in light of possible PEO/cathode interfacial stability concepts.

Towards extreme fast charging of 4.6 V LiCoO2 via mitigating high-voltage kinetic hindrance

High-voltage LiCoO2 (LCO) is an attractive cathode for ultra-high energy density lithium-ion batteries (LIBs) in the 3 C markets. However, the sluggish lithium-ion diffusion at high voltage significantly hampers its rate capability. Herein, combining experiments with density functional theory (DFT) calculations, we demonstrate that the kinetic limitations can be mitigated by a facial Mg2++Gd3+ co-doping method. The as-prepared LCO shows significantly enhanced Li-ion diffusion mobility at high voltage, making more homogenous Li-ion de/intercalation at a high-rate charge/discharge process. The homogeneity enables the structural stability of LCO at a high-rate current density, inhibiting stress accumulation and irreversible phase transition. When used in combination with a Li metal anode, the doped LCO shows an extreme fast charging (XFC) capability, with a superior high capacity of 193.1 mA h g−1 even at the current density of 20 C and high-rate capacity retention of 91.3% after 100 cycles at 5 C. This work provides a new insight to prepare XFC high-voltage LCO cathode materials.

Controlling Cell Components to Design High-Voltage All-Solid-State Lithium-Ion Batteries.

All-solid-state batteries with solid ionic conductors packed between solid electrode films can release the dead space between them, enabling a greater number of cells to stack, generating higher voltage to the pack. This Review is focused on using high-voltage cathode materials, in which the redox peak of the components is extended beyond 4.7 V. Li-Ni-Mn-O systems are currently under investigation for use as the cathode in high-voltage cells. Solid electrolytes compatible with the cathode, including halide- and sulfide-based electrolytes, are also reviewed. Discussion extends to the compatibility between electrodes and electrolytes at such extended potentials. Moreover, control over the thickness of the anode is essential to reduce solid-electrolyte interphase formation and growth of dendrites. The Review discusses routes toward optimization of the cell components to minimize electrode-electrolyte impedance and facilitate ion transportation during the battery cycle.