High-voltage Cathode Materials Research Articles

Enhanced Thermal Stability and Conductivity of FeF3 Using Ni-Coated Carbon Composites: Application as High-Temperature Cathodes in Thermal Batteries.

Cathode active materials and conductive additives for thermal batteries operating at high temperatures have attracted research interest, with a particular focus on compounds offering high thermal stability. Recently, FeF3 has been proposed as a candidate for high-voltage cathode materials; however, its commercialization is hindered by its low conductivity. In this study, conductive additives, such as Ni-coated carbon composites (multi-walled carbon nanotubes (MWCNTs) and carbon black (CB)), were utilized to enhance the thermal stability and conductivity of FeF3. The incorporation of metal-carbon conductive additives in the FeF3 composite increased the thermal stability by more than 10 wt.% and ensured high capacity upon conductivity enhancement. The FeF3@Ni/MWCB 15 wt.% composite containing 30 wt.% Ni exhibited a discharge capacity of ∼86% of the theoretical capacity of 712 mAh/g. The use of Ni-coated carbon-based conductive additives will allow the application of FeF3 as an effective high-temperature cathode material for thermal batteries.

Investigation of Na7V3(P2O7)4/carbon composite as cathode material for sodium-ion battery: Influences of carbon additives and voltage windows

A sequentially processed method is developed to prepare a high-voltage cathode material sodium vanadium diphosphate Na7V3(P2O7)4 for Na-ion battery. We find that the growth of Na7V3(P2O7)4 generally introduces growth orientation due to their hybrid ionic and covalent bonding. The crystal growth of the diphosphate prefers to grow perpendicular to [002] direction, leading to an increase of the diffusion length of Na+ ion. To regulate the growth of crystal, three kinds of carbon additives, graphene oxide, Cabot carbon black and Ketjen carbon black are adopted to tune the morphologies of Na7V3(P2O7)4 to further improve its electrochemical performances. The morphologies and physicochemical properties of carbon additives and corresponding prepared Na7V3(P2O7)4 are both well characterized to clarify the effects of carbon additives on the growth process. We find that the Cabot carbon black can dramatically weaken the oriented growth direction and produce fine morphology. By adding Cabot carbon black to the sequential process, the reversible capacity of Na7V3(P2O7)4 can reach to 76 mAh g−1 with good cyclability within the voltage window of 2–4.5 V. An average voltage of 3.8 V can be obtained due to the strong inductive effect of diphosphate group.

A 3.5 V-class organic sodium-ion battery using a croconate cathode

Sodium-ion batteries (SIBs) based on organic cathode materials have received considerable attention owing to high theoretical capacities, cost-effectiveness, and raw material abundance. However, high-voltage organic cathodes have been rarely investigated for SIBs mainly due to their electrical insulation and dissolution in electrolytes. In this study, sodium croconate (C5O5Na2) is utilized as a high-voltage cathode material for SIBs, designing an interface using a functionalized multi-walled carbon nanotube (MWCNT). The composite C5O5Na2 cathode with carboxylic-acid-functionalized-(COOH–) MWCNT exhibits a 3.5 V-class high-voltage redox activity with a cycle performance higher than that of non-functionalized MWCNT/C5O5Na2 composite cathodes; the capacity retention ratio is improved from 0 % to 34 % after 30 cycles at 0.1C. Raman, X-ray photoelectron spectroscopy, and solid-state nuclear magnetic resonance reveal the formation of hydrogen bonding between COOH groups on MWCNT and carbonyl groups in C5O5Na2 molecules; leading to suppression of organic molecules and improvement on the cycle performance. A full cell assembled with the C5O5Na2/COOH–MWCNT cathode and a hard carbon anode also shows a high-voltage redox plateau at around 3.5 V and a 1st discharge capacity of 123 mAh g−1 at 1C. These results suggest the feasibility of developing a high-energy-density storage system using completely common-metal components.

Rapid preparation of cobalt-free lithium rich cathode materials with layered structure and excellent performance via capillary microreactors

High voltage and high energy density cathode materials are the future development trend of power batteries. Li-and Mn-rich layered oxide (LMR) materials exhibit high capacity, low cost, and environmental friendliness, making them a promising cathode material for the next generation of lithium-ion batteries. In this study, a continuous-flow process for rapid co-precipitation synthesis of LMR precursor (Mn0.75Ni0.25CO3) in capillary microreactors was developed. Due to the good mixing characteristics of the microreactor (tm=54 ms), Mn0.75Ni0.25CO3 displays a complete spherical morphology and uniform elemental distribution without adding any complexing agent during the synthesis. The reaction time can be controlled within 11.78 s. The prepared Li1.2Mn0.6Ni0.2O2 (LMR) cathode exhibits excellent properties with a high initial discharge capacity of 266.52 mAh•g−1 at 0.1C and a superior capacity retention of 93.7 % after 200 cycles at 1C. This work demonstrates that microfluidic technology presents a viable and promising approach for quickly producing lithium battery cathode precursors.

A Study on Corrosion of Al-Clad Coin Cell Cases in High-Voltage Li-Ion Battery

Aluminum-coated (Al-Clad) coin cell case has long been introduced to evaluate high-voltage cathode materials and electrolytes in battery research. However, our study on graphite/LiNi0.80Co0.10Mn0.10O2 (Gr/NCM811) coin cells indicates that the Al-Clad case resulted in even worse performance than the pristine stainless steel (SS) case. Post-mortem observation finds that the Al-Clad case was severely corroded, while the SS case seems to remain intact. To understand this unusual phenomenon, the corrosion behavior of the Al-Clad cases in LiPF6 electrolyte and lithium bis(fluorosulfonyl)imide (LiFSI) electrolyte, respectively, is studied. It is shown that the coating of Al on the Al-Clad cases is not dense, allowing liquid electrolytes to permeate through and contact the underlying SS core case, forming galvanic cells between the Al coating and the SS core case. At high potentials, the galvanic cells reduce the over-potential of Al oxidation, promoting corrosion of the Al coating. As such, the Al coating does not protect the underlying SS core case, oppositely, making the corrosion of itself more severe. The results of this work reveal that to support high-voltage applications, the coating of Al on the Al-Clad cases must be dense, otherwise, it makes the corrosion worse.

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.