LiNi0.5Mn1.5O4 Research Articles

Enabling structural and interfacial stability of 5 V spinel LiNi0.5Mn1.5O4 cathode by a coherent interface

Spinel LiNi0.5Mn1.5O4 (LNMO), a 5 V class high voltage cathode, has been regarded as an attractive candidate to further improve the energy density of lithium-ion battery. The issue simultaneously enabling side stability and maintaining high interfacial kinetics, however, has not yet been resolved. Herein, we design a coherent Li1.3Al0.3Ti1.7(PO)4 (LATP) layer that is crystally connected to the spinel LNMO host lattices, which offers fast lithium ions transportation as well as enhances the mechanical stability that prevents the particle fracture. Furthermore, the inactive Li3BO3 (LBO) coating layer inhibits the corrosion of transition metals and continuous side reactions. Consequently, the coherent-engineered LNMO-LATP-LBO cathode material exhibits superior electrochemical cycling stability in a window of 3.0–5.0 V, for example a high-capacity retention that is 89.7% after 500 cycles at 200 mA g−1 obtained and enhanced rate performance (85.1 mA h g−1 at 800 mA g−1) when tested with a LiPF6-based carbonate electrolyte. Our work presents a new approach of engineering 5 V class spinel oxide cathode that combines interfacial coherent crystal lattice design and surface coating.

Stabilizing High-Voltage LiNi0.5 Mn1.5 O4 Cathodes for High Energy Rechargeable Li Batteries by Coating With Organic Aromatic Acids and Their Li Salts.

Here, three types of surface coatings based on adsorption of organic aromatic acids or their Li salts are applied as functional coating substrates to engineer the surface properties of high voltage LiNi0.5 Mn1.5 O4 (LNMO) spinel cathodes. The materials used as coating include 1,3,5-benzene-tricarboxylic acid (trimesic acid [TMA]), its Li-salt, and 1,4-benzene-dicarboxylic acid (terephthalic acid). The surface coating involves simple ethanol liquid-phase mixing and low-temperature heat treatment under nitrogen flow. In typical comparative studies, TMA-coated (3-5%) LNMO cathodes deliver >90% capacity retention after 400 cycles with significantly improved rate performance in Li-coin cells at 30 °C compared to uncoated material with capacity retention of ≈40%. The cathode coating also prevents the rapid drop in the electrochemical activity of high voltage Li cells at 55 °C. Studies of high voltage full cells containing TMA coated cathodes versus graphite anodes also demonstrate improved electrochemical behavior, including improved cycling performance and capacity retention, increased rate capabilities, lower voltage hysteresis, and very minor direct current internal resistance evolution. In line with the highly positive effects on the electrochemical performance, it is found that these coatings reduce detrimental transition metal cations dissolution and ensure structural stability during prolonged cycling and thermal stability at elevated temperatures.

Improving the electrochemical performance of single crystal LiNi0.5Mn1.5O4 cathode materials by Y–Ti doping and unannealing process

In recent years, due to the rising price of cobalt, people have been increasingly interested in LiNi0.5Mn1.5O4 (LNMO) cathode materials, and many studies researches have been carried out on the preparation and modification of LNMO. However, the codoping of Y and Ti and the choice of annealing and unannealing processes after doping are less explored. In this study, single-crystal LNMO particles and Y, Ti-doped LiNi0.45Mn1.45O4 particles were prepared by a simple sol-gel method under annealing and unannealing processes, respectively. Four samples were analyzed by X-ray powder diffraction, Raman spectra, Fourier transform infrared spectroscopy and electron paramagnetic resonance. By these means, it was found that the samples doped and not annealed had the largest amount of disordered structures and oxygen vacancies (OVs). Scanning electron microscopy showed that the doped and unannealed samples had more exposed (100) crystal planes than the other samples, and after multiple cycles, this sample had the smoothest surface morphology. Electrochemical tests show that the doped and unannealed samples exhibit excellent electrochemical performance, with a Coulombic efficiency of 93.94% in the first cycle, a specific capacity of 126.74 mAh⋅g−1 after 500 cycles at a rate of 1 C, and a specific capacity of 126.74 mAh⋅g−1 at a rate of 5 C. After 500 cycles, the specific capacity is 111.1 mAh⋅g−1.

Insight into the cation migration and surface structural evolution of spinel LiNi0.5Mn1.5O4 cathode material for lithium-ion batteries

High-voltage spinel LiNi0.5Mn1.5O4 (LNMO) is considered to be a promising cathode material for electric vehicles (EV) and hybrid electric vehicles (HEVs). Nevertheless, the structural transformation under a deep discharge voltage is still ambiguity. Herein, we report detailed studies of structural change of LNMO cathode under a wide voltage range of 5.0–1.5 V cycling by using synchrotron-based X-ray absorption spectroscopy, aberration-corrected scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). The fundamental findings demonstrate that LNMO would undergo a complex phase transformation from cubic to tetragonal during deep discharge to a voltage lower than 3 V. It gives rise to a further reduction of Mn4+ to Mn3+ and this serious structural distortion leads to the formation of Li2Mn2O4-type tetragonal phase with space group of I41/amd, which is also confirmed by XANES simulations and density functional theory (DFT) calculations. Meanwhile, migration of Ni ions toward the surface from bulk lattice, leading to the rock-salt NiO phase formation with a space group of Fm-3 m. Finally, these observed evolutions on the surface are associated to the fast capacity fading for LNMO under such a wide voltage range. This work provides insight into understanding the capacity degradation mechanism of spinel cathodes and would inspire us to further design high-performance cathode materials for advanced lithium-ion batteries.

Electrochemical performance of high voltage LiNi0.5Mn1.5O4 based on environmentally friendly binders

The extended cyclability of LiNi0.5Mn1.5O4 (LNMO) electrodes featuring different water-based binders is here reported. LNMO electrodes with guar gum (GG) binders show a relatively stable cycle performance at 0 °C and room temperature. However, water-based binders exhibit higher capacity fade than those with polyvinylidene fluoride (PVdF) binder at 50 °C. Although PVdF binder has a lower adhesion force than CMC and GG; PVdF-based electrodes exhibit better capacity retention than those with water-based binders at 50 °C over 1000 cycles. Finally, operando Differential Electrochemical Mass Spectrometry (DEMS) experiments were carried out to analyze the evolution of volatile decomposition products formed over cycling at 1C and 30 °C of CMC-, GG- and PVdF-based LNMO electrodes. CO2 and H2 gas evolutions increase remarkably at both high temperatures and high potentials, i.e., ~ 4.7 V.

Tuning the Electronic, Ion Transport, and Stability Properties of Li-rich Manganese-based Oxide Materials with Oxide Perovskite Coatings: A First-Principles Computational Study.

Lithium-rich manganese-based oxides (LRMO) are regarded as promising cathode materials for powering electric applications due to their high capacity (250 mAh g–1) and energy density (∼900 Wh kg–1). However, poor cycle stability and capacity fading have impeded the commercialization of this family of materials as battery components. Surface modification based on coating has proven successful in mitigating some of these problems, but a microscopic understanding of how such improvements are attained is still lacking, thus impeding systematic and rational design of LRMO-based cathodes. In this work, first-principles density functional theory (DFT) calculations are carried out to fill out such a knowledge gap and to propose a promising LRMO-coating material. It is found that SrTiO3 (STO), an archetypal and highly stable oxide perovskite, represents an excellent coating material for Li1.2Ni0.2Mn0.6O2 (LNMO), a prototypical member of the LRMO family. An accomplished atomistic model is constructed to theoretically estimate the structural, electronic, oxygen vacancy formation energy, and lithium-transport properties of the LNMO/STO interface system, thus providing insightful comparisons with the two integrating bulk materials. It is found that (i) electronic transport in the LNMO cathode is enhanced due to partial closure of the LNMO band gap (∼0.4 eV) and (ii) the lithium ions can easily diffuse near the LNMO/STO interface and within STO due to the small size of the involved ion-hopping energy barriers. Furthermore, the formation energy of oxygen vacancies notably increases close to the LNMO/STO interface, thus indicating a reduction in oxygen loss at the cathode surface and a potential inhibition of undesirable structural phase transitions. This theoretical work therefore opens up new routes for the practical improvement of cost-affordable lithium-rich cathode materials based on highly stable oxide perovskite coatings.

Addressing Mn Dissolution in High‐Voltage LiNi0.5Mn1.5O4 Cathodes via Interface Phase Modulation

AbstractSpinel LiNi0.5Mn1.5O4 (LNMO), high‐voltage and high‐power density, is a very promising cathode candidate. Nevertheless, its lack of cycling stability has historically been long accepted as an inherent issue. Based on the above problem, a strategy is initiated to directly address Mn dissolution and unstable interface structure. A beneficial solid‐phase reaction occurs at the LNMO interface, transforming the spinel phase into two functional phases. One is the layered phase that provides electrochemical activity and supports charge transport. The other is the rock‐salt like phase induced by Li/Mn exchange that can inhibit the dissolution of Mn and provide inert protection. The Li/Mn exchange structure increases the diffusion energy barriers of Mn, which restrains the loss of Mn, proven by the bond valence sum calculation. The two phases are modulated successfully at the LNMO interface to balance the stable material structure and excellent charge transfer, obtaining a sample with excellent electrochemical performance. The capacity retention rate of modified LNMO is 15% higher than that of the pristine sample after 500 cycles. The preparation method does not utilize any dopants or coatings and can play a guiding role in addressing issues regarding structural stability and electrochemical performance for cathode materials.

Probing the Electrochemical Li Insertion–Extraction Mechanism in Sputtered LiNi0.5Mn1.5O4 Thin Film Cathode for Li‐Ion Microbattery

AbstractDue to its great theoretical capacity (147 mAh g−1) and high operating potential (4.7 V vs Li+/Li), Co‐free spinel LiNi0.5Mn1.5O4 (LNMO) is one of the most promising thin film cathodes allowing designing Li‐ion micro‐batteries with a high specific energy. In this work, the Li extraction–insertion mechanism in sputtered LNMO thin films is investigated by X‐ray diffraction and Raman spectroscopy during the first electrochemical cycle. A one‐step phase transition involving two cubic phases is revealed, consisting of a wide solid solution region (0.3 ≤ x ≤ 1 in LixNMO) and a narrow biphasic domain (0 < x ≤ 0.3). Remarkably, significant variations are observed in the Raman spectra, which are linked to the activity of the Ni redox system at 4.7 V. It is demonstrated that an appropriate analysis of the bands corresponding to pure Ni–O stretching modes leads to an accurate estimation of the electrode states of charge and depth of discharge, which opens the way for a reliable quantification of the self‐discharge phenomenon. The mechanism of Li extraction insertion here pictured for the first time for LNMO thin layers is consistent with their disordered nature and accounts for their good electrochemical performance.

Enabling a Co-Free, High-Voltage LiNi0.5Mn1.5O4 Cathode in All-Solid-State Batteries with a Halide Electrolyte

One approach to increase the energy density of all-solid-state batteries (ASSBs) is to use high-voltage cathode materials. The spinel LiNi0.5Mn1.5O4 (LNMO) cathode is one such example, as it offers a high reaction potential (close to 5 V). Moreover, it is a Co-free cathode system, which makes it an environmentally friendly and a low-cost alternative. However, several challenges must be addressed before it can be properly adopted in ASSB technologies. Herein, we reveal that lithium argyrodite (Li6PS5Cl), a sulfide solid-state electrolyte (SSE), possesses intrinsic chemical incompatibility with the LNMO cathode. We demonstrate the necessity of using a halide SSE, Li3YCl6 (LYC), through careful analysis of the LNMO/SSE interface. Moreover, we emphasize the necessity of applying a protective coating layer to LNMO particles, even when halide SSEs are used. Furthermore, the chemical phenomena involving LYC in the oxidative environment of LNMO are analyzed, including a comparison between coated and uncoated LNMO particles.

5V Solid-State Lithium Batteries Using Garnet-Based Electrolytes and LiNi0.5Mn1.5O4 Spinel Cathode Composite

There is an ever increasing demand to increase the gravimetric and volumetric energy density of Lithium batteries as well as enhancing their safety cycle life and lower safety. Solid-State batteries (SSB) enjoy a great attention nowadays due to their potential to meet all those requirements and power the EV revolution. The use of solid electrolytes (SE) in commercial batteries has been solely limited to polymer electrolytes based on poly(ethylene oxide), PEO, coupled with LiFePO4 (LFP) that are limited by the oxidative stability of PEO to < 3.6 V and the low potential of LFP at 3.4 V. The commercial cells are cycled at high temperature (45 ⁰C) to overcome the modest ambient ionic conductivity of the SE and under a stack pressure and a cathode composite to overcome the high interfacial resistances of the solid-solid interfaces. A cathode composite is made of conventional cathode components with a "catholyte" added to the formulation. The catholyte is made of an optimized amount of an ionic conductor that is mostly derived from the solid electrolyte formulation. Very recent studies by our research group (1) and others (2) have shown that higher voltage cells can be made by using garnet or perovskite-based ceramic/polymer composites and LiNi0.5Mn0.3Co0.2O2 (NMC532) or LiNi0.6Mn0.2Co0.2O2 (NMC 622) layered cathodes reaching 4.2 V and can operate for few cycles. Herein, we extend the work in order to further increase the voltage of the SSB cells by using LiNi0.5Mn1.5O4 (LNMO) spinel cathode with its high potential of 4.7 V. The Tantalum-doped Lithium Lanthanum Zirconate, Li6.4La3Zr1.4Ta0.6O12 (Ta-doped LLZO, LLZTO), of the garnet family of solid electrolytes has been selected as a SE due to their high ambient ionic conductivity, wide electrochemical stability window and good chemical stability against Li metal. PEO and other compatible polymers have been used to formulate composite SEs in thin films and their properties were studied and compared with LLZTO pellets. Cells have been made using composite cathode formulations composed of LNMO cathode as an active material, carbon black, conventional and novel binders and a SE-based and proprietary catholyte coupled with the SE films or pellets and thick/thin Li films. The short-term cycling performance of the cells assembled with selected SEs and composite cathodes along with other electrochemical results will be presented.

The Correlation between Structure, Surface, and Performance in Fe- and Mg-Substituted LiNi0.5Mn1.5O4 Cathodes

A need for lithium-ion cathodes that have a reduced dependence on scarce elements, such as cobalt, has been prompted by surge in eco-consciousness over the past decade. The spinel-type LiNi0.5Mn1.5O4 (LNMO) cathodes, with high operating voltages (ca. 4.7V vs Li+/Li) and energy densities (ca. 650 Wh kg-1), have received particular attention for this reason.1 Poor cycling stability, however, which arises from structural instabilities, electrolyte degradation, surface densification and loss of active material through transition metal dissolution, limits their widespread adoption.2 Elemental substitution has been employed to overcome such limitations, in which improved cycling stability has been observed. In such samples, the segregation of substituents to the cathode surface has been reported, yet the effect of surface segregation on the local atomic structure and surficial reactivity of the cathodes is under-researched.3 To further explore these areas, Fe- and Mg-substituted LNMO samples have been synthesised. Despite lower initial capacity, Mg-substituted LNMO exhibits significantly improved cycling stability over 300 cycles at 50°C. A combination of x-ray and neutron diffraction, neutron pair distribution function analysis, and x-ray absorption and photoelectron spectroscopy are used to explore the complex relationships between bulk structure, local structure, surface reactivity and performance in Fe- and Mg-substituted LNMO cathodes. References Liang, G., Peterson, V.K., See, K.W., Guo, Z., and Pang, W.K. (2020). Developing high-voltage spinel LiNi 0.5 Mn 1.5 O 4 cathodes for high-energy-density lithium-ion batteries: current achievements and future prospects . J. Mater. Chem. A.Ma, J., Hu, P., Cui, G., and Chen, L. (2016). Surface and Interface Issues in Spinel LiNi0.5Mn1.5O4: Insights into a Potential Cathode Material for High Energy Density Lithium Ion Batteries. Chem. Mater. 28, 3578–3606.Shin, D.W., Bridges, C.A., Huq, A., Paranthaman, M.P., and Manthiram, A. (2012). Role of Cation Ordering and Surface Segregation in High-Voltage Spinel LiMn LiMn 1.5Ni 0.5-xM xO 4(M = Cr, Fe, and Ga) Cathodes for Lithium-Ion Batteries. Chem. Mater. 24, 3720–3731. Figure 1

Novel Acrylonitrile-Based Polymers for Solid–State Polymer Electrolyte and Solid-State Lithium Ion Battery

Rechargeable lithium-ion batteries (LIBs) involving lithium metal oxides, liquid electrolyte and graphite have been widely used in portable electronic devices due to their relatively high energy density and long cycle life. These desirable features make LIBs very attractive as the power source for electronic devices, hybrid electric vehicles (HEVs) and electric vehicles (EVs) applications [1, 2]. For future EV applications, higher energy density of LIBs up to 360 Wh kg-1 is required. Currently, the energy density of the state-of-the-art LIBs using conventional graphite anode, LiFePO4 (denoted as LFP) or LiNi0.5Co0.2Mn0.3O2 (NCM523) cathodes and 1-1.2 M LiPF6 in organic carbonate electrolytes provide practically achievable energy densities of up to around 200-260 Wh kg−1 [3]. When commercial graphite anodes are used, LiNi0.8Co0.15Al0.05O2 (NCA), LiNi0.8Co0.1Mn0.1O2 (NCM811), LiNi0.5Mn1.5O4 (LNMO) and LiNiPO4 (LNP) cathode based batteries with high-voltage provide energy densities of 354, 338, 351 and 414 Wh kg-1, respectively. However, LIBs using these high-voltage cathode materials and the organic carbonate electrolytes exhibit quite low thermal stability and tend to catch fire or even explode when abnormal charge/discharge cycling or accidental penetration of cells occurs, which greatly limits the automotive applications. When replacing graphite with a Li metal anode, the energy densities of all battery systems can be enhanced significantly due to the highest theoretical specific energy density (3860 mAh g-1) among all anode materials for rechargeable LIBs. Nevertheless, commercial LIBs are prone to cause safety problems due to the safety concern arising from Li dendrite growth in liquid organic electrolytes [4-6].The promising solid-state LIBs offer high thermal stability (i.e., low risk in catching fire), high energy density, wide electrochemical stability window and less environmental impact. A competent electrolyte is the key component of solid-state LIBs. The solid-state electrolyte materials are mainly classified as solid polymer electrolytes (SPEs), inorganic solid electrolytes (ISEs), and organic/inorganic composite electrolytes. ISEs include oxide-based and sulfide-based materials [7, 8], which show very high ionic conductivity (10-2 – 10-3 S cm-1). Furthermore, the lithium ion transference number is close to 1. However, the major limitation factors of practical solid-state LIB applications are the large interfacial impedance between electrode and ISE and the difficulty of processing [9]. Considering processability, mechanical flexibility, interfacial compatibility and electrochemical stability, one prefers SPEs to the inorganic ceramic electrolytes. Nevertheless, SPEs have low ion conductivities (10−7 − 10−5 S cm−1 near room temperature) and most of the Li+ transference numbers are lower than 0.5 [10, 11]. The major requirements for SPEs include high ionic conductivity and transference number at room temperature, wide electrochemical potential window, high mechanical strength and excellent thermal stability. However, the ion conductivity is the most important (> 10-4 S cm-1 at room temperature desired) and should be considered first. The coordinating groups of a good polymeric host are expected to interact with Li+ and facilitate dissociation.In this study, we prepared various novel acrylonitrile-based polymers (e.g., acrylonitrile/acrylate copolymer and polymer with two pendant groups b-cyano ethyl ether (-O-CH2CH2-CN) sulfonate alkyl ether (-O-(CH2)3SO3Li). The corresponding SPEs comprising acrylonitrile-based polymer and ca. 50 wt.% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) with high ionic conductivity (up to 10-3 S cm-1) at room temperature, high ion transfer number (up to 0.45) and large electrochemical potential window (oxidation stability > 5 V vs. Li+/Li) achieved. The selected SPEs were used as the separator in solid-state batteries with LiFePO4 as the cathode and Li foil as the anode; and long-term cycle stability of solid-state LIB was achieved. The polymers and corresponding SPEs were characterized by using DSC, SEM, XRD and FTIR measurements. Ionic conductivities of SPEs were determined from electrochemical impedance spectroscopy results. The linear sweep voltammetry technique was adopted to measure the oxidation stability window of SPE, and the Evans-Vincent-Bruce method was used to determined ion transfer number.

Unraveling the Stable Cathode Electrolyte Interface in all Solid‐State Thin‐Film Battery Operating at 5 V

AbstractSpinel‐type LiNi0.5Mn1.5O4 (LNMO) is one of the most promising 5 V‐class cathode materials for Li‐ion batteries that can achieve high energy density and low production costs. However, in liquid electrolyte cells, the high voltage causes continuous cell degradation through the oxidative decomposition of carbonate‐based liquid electrolytes. In contrast, some solid‐state electrolytes have a wide electrochemical stability range and can withstand the required oxidative potential. In this work, a thin‐film battery consisting of an LNMO cathode with a solid lithium phosphorus oxynitride (LiPON) electrolyte is tested and their interface before and after cycling is characterized. With Li metal as the anode, this system can deliver stable performance for 600 cycles with an average Coulombic efficiency &gt;99%. Neutron depth profiling indicates a slight overlithiated layer at the interface prior to cycling, a result that is consistent with the excess charge capacity measured during the first cycle. Cryogenic electron microscopy further reveals intimate contact between LNMO and LiPON without noticeable structure and chemical composition evolution after extended cycling, demonstrating the superior stability of LiPON against a high voltage cathode. Consequently, design guidelines are proposed for interface engineering that can accelerate the commercialization of a high voltage cell with solid or liquid electrolytes.

Ion-Permselective Polyphenylene Sulfide-Based Solid-State Separator for High Voltage LiNi0.5Mn1.5O4 Battery

The decomposition of commonly used commercial electrolytes under high voltage and the continuous side reactions at the graphite anode make the rapid capacity decay of LiNi0.5Mn1.5O4(LNMO)/graphite full cell during cycling. In this work, we adopt ion-permselective polyphenylene sulfide-based solid state separator (PPS-SSS) for LNMO batteries, PPS-SSS can effectively prevent the proton diffusion, block the HF generated on the LNMO cathode from attacking the anode SEI layer, and mitigate the Mn2+ transfer. The PPS-SSS with anodic polyethylene (PE) protection (PE-PPS-CSSS) significantly improved the cycling performance of LNMO batteries. In the LNMO/Li half-cell system, 93% capacity retention rate can be achieved after 140 cycles at 0.5 C, and in the LNMO/graphite full-cell system, 85% of the initial capacity can be maintained after 100 cycles. Moreover, flight secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS) are applied to explore the interfacial reactions of LNMO/graphite batteries and reveal the key mechanism for the stable cycling using PPS-SSS.

Paving Pathways Toward Long‐Life Graphite/LiNi0.5Mn1.5O4 Full Cells: Electrochemical and Interphasial Points of View

AbstractThe high‐voltage spinel cathode LiNi0.5Mn1.5O4 (LNMO) with no cobalt and low nickel content is promising for lithium‐ion batteries due to its high energy and power densities, good thermal stability, and low cost. However, its high operating voltage (≈4.7 V) results in a decomposition of the electrolyte, severe chemical crossover, and deterioration of electrode‐electrolyte interphases (EEIs), hindering its practical viability. It is demonstrated here that by electrochemically pre‐cycling the graphite in an electrolyte containing 30 wt.% fluoroethylene carbonate, a robust LiF‐rich artificial solid electrolyte interphase can be constructed for surface protection; on the other hand, an electrochemical pre‐lithiation of Fe‐doped LNMO serves as a lithium source for graphite at a full‐cell voltage of 2.6 V. As a result, the full cells with the as‐modified electrodes deliver a high capacity of 129 mA h g−1 with an excellent capacity retention of 93% after 200 cycles, vastly outperforming the full cells with fresh electrodes (120 mA h g−1 initial capacity with 78% retention). Finally, pathways toward long‐life graphite||LNMO full cells are pictured based on the inspirations from the electrochemical modifications and in‐depth analyses of the EEIs in this study.

In Situ Induced Lattice-Matched Interfacial Oxygen-Passivation-Layer Endowing Li-Rich and Mn-Based Cathodes with Ultralong Life.

The high capacity of Li-rich and Mn-based (LRM) cathode materials is originally due to the unique hybrid anion- and cation redox, which also induces detrimental oxygen escape. Furthermore, the counter diffusion of released oxygen (into electrolyte) and induced oxygen vacancies (into the interior bulk phase) that occurs at the interface will cause uncontrolled phase collapse and other issues. Therefore, due to its higher working voltage (>4.7V) than the activation voltage of lattice oxygen in LRM (≈4.5V), the anion-redox-free and structurally consistent cobalt-free LiNi0.5 Mn1.5 O4 (LNMO) is selected to in situ construct a robust, crystal-dense and lattice-matched oxygen-passivation-layer (OPL) on the surface of LRM particles by the electrochemical delithiation to protect the core layered components. As expected, the modified sample displays continuously decreasing interfacial impedance and high specific capacity of 135.5 mAh g-1 with a very small voltage decay of 0.67mV per cycle after 1000 cycles at 2 C rate. Moreover, the stress accumulation during cycling is mitigated effectively. This semicoherent OPL strengthens the surface stability and interrupts the counter diffusion of oxygen and oxygen vacancies in LRM cathode materials, which would provide guidance for designing high-energy-density layered cathode materials.

Unveiling the role of Ti substitution in improving safety of high voltage LiNi0.5Mn1.5-xTixO4 cathode material by ameliorating Structure-stability and enhancing Elevated-temperature properties

The proposal of net-zero emissions policy promotes the research on safety property of cathode material in lithium ion batteries. Herein, to improve the safety of high voltage LiNi0.5Mn1.5O4(LNMO) as cathode material in lithium ion batteries, Ti4+ ions were doped into LNMO(LNMTO) and the enhancement mechanisms on safety property were investigated from aspects of structure stability and elevated-temperature properties by experimental and theoretical study. In experimental, the influence of Ti4+ doping on cathode/electrolyte interface stability and cathode thermal stability is explored by differential scanning calorimetry test(DSC), thermal diffusion and In-situ-XRD. Ti4+ doping can effectively improve the structure-stability of LNMO by infusing the stronger Ti-O bands, promoting thermal diffusion and suppressing the unexpected two-phase reactions. Compared with LNMO, LNMTO exhibits superior cycling stability at elevated-temperature with the 100th capacity of 124.1 mAh·g−1, which is equal to 98.8% of the 1st discharge capacity under 2C at 55 °C. Furthermore, we also verified the effectiveness of Ti4+ doping on improving thermal stability in LNMO/Li4Ti5O12(LTO) full cells. This work systematically investigates the effect of Ti4+ doping on safety of LNMO from aspects of structure-stability and elevated-temperature properties, which can be easily stretched into other cathode materials and speed up wider application of LIBs.

Synergistic effect of doping and surface engineering on LiNi0.5Mn1.5O4 and its application as a high-performance cathode material for Li-ion batteries

In this study, we synthesize V5+-doped LiNi0.5Mn1.5O4 (LNMO) and subject it to SiO2 surface modification using a coprecipitation method. The synergistic effect of ion doping and interfacial engineering improves the electrochemical properties of LNMO by accelerating its redox kinetics and prolonging its cycling life. The experimental results and density functional theory simulation data indicate that V5+-ion doping caused the Fermi level of LNMO to shift toward the conduction band, thereby narrowing the bandgap of LNMO because of the n-type doping effect. However, the introduction of V5+ ions prevents Li + -ion migration in LNMO, which hinders the ion intercalation–deintercalation process of LNMO cathodes. Therefore, the V5+-doped LNMO compound with optimal V5+-ion doping concentration was expected to present the highest rate capability. In addition, SiO2 surface modification provides a protective layer that inhibits metal dissolutions and significantly improves cathode cycling stability. Owing to the synergistic effect of doping and interfacial modification, the fabricated LNMO cathode presented remarkable energy storage capacity with discharge capacities of 133/118.8 mAh/g at 0.2/10 C and a capacity retention of 87.9% after 200 cycles at 4 C.

Elucidating the function of modified carbon blacks in high-voltage lithium-ion batteries: impact on electrolyte decomposition

We report on the improved electrochemical performance of a high-voltage LiNi0.5Mn1.5O4 (LNMO) cathode using surface-modified carbon blacks (CBs) as conductive agents. Facile modifications of CBs were achieved using thermal, urea-based hydrothermal, and acid oxidation treatments. The material properties of the modified CBs, LNMO-based electrode surface, and electrolyte compositions were investigated and correlated. Based on the distribution of the decomposition deposits on the surface of the electrode, it is confirmed that CB, rather than the LNMO active material, dominates the electrolyte decomposition site at a high voltage, owing to its relatively high surface area for the reaction. Additionally, compared with the pristine CB, the hydrothermally treated N-doped CB (HCB) improves the electrochemical performance of the LNMO cathode, although the thermally treated sample exhibits the most adverse influence, followed by the oxidized one. The LNMO/HCB cathode attains optimum capacity retention (approximately 95%) for 100 cycles (1 C) and a high rate capability (70%, 5 C/0.2 C), corresponding to a lowered resistance at the cathode–electrolyte interface. Furthermore, HCB with a limited specific surface area and increased defects, as well as additional pyrrolic-N and pyridinic-N groups, substantially reduces the decomposition deposits on the surface of the electrode and the decomposition products in the electrolyte. These phenomena account for the improved electrochemical performance of the LNMO/HCB cathode.

Advanced perfluorinated electrolyte with synergistic effect of fluorinated solvents for high-voltage LiNi0.5Mn1.5O4/Li cell

A series of designed fluorinated electrolytes with single or multiple fluorinated solvents were developed for the application of high-voltage lithium second batteries. The synergistic effect of various fluorinated solvents evidently enhance the reversible capacity, cycle and rate performance of the LiNi0.5Mn1.5O4 (LNMO)/Li cell, profitted from superior durability of the electrolyte to resist oxidation (despite weakened ionic conductivity), successful surface modification on the LNMO cathode to suppress parasitic reaction, and improved Li metal compatibility to aviod anode corrosion. Theoretical calculation results reveal that the competitive coordination among different solvents inevitably regulates the solvation structure of Li ion, redox capability of the electrolyte and then interfacial chemistry on both electrodes.