High Voltage Spinel Cathode Materials Research Articles

High-Voltage Spinel Cathode Materials: Navigating the Structural Evolution for Lithium-Ion Batteries.

High-voltage LiNi0.5Mn1.5O4 (LNMO) spinel oxides are highly promising cobalt-free cathode materials to cater to the surging demand for lithium-ion batteries (LIBs). However, commercial application of LNMOs is still challenging despite decades of research. To address the challenge, the understanding of their crystallography and structural evolutions during synthesis and electrochemical operation is critical. This review aims to illustrate and to update the fundamentals of crystallography, phase transition mechanisms, and electrochemical behaviors of LNMOs. First, the research history of LNMO and its development into a LIB cathode material is outlined. Then the structural basics of LNMOs including the classic and updated views of the crystal polymorphism, interconversion between the polymorphs, and structure-composition relationship is reviewed. Afterward, the phase transition mechanisms of LNMOs that connect structural and electrochemical properties are comprehensively discussed from fundamental thermodynamics to operando dynamics at intra- and inter-particle levels. In addition, phase evolutions during overlithiation as well as thermal-/electrochemical-driven phase transformations of LNMOs are also discussed. Finally, recommendations are offered for the further development of LNMOs as well as other complex materials to unlock their full potential for future sustainable and powerful batteries.

Speciation of Transition Metal Dissolution in Electrolyte from Common Cathode Materials

Significant capacity loss has been observed across extended cycling of lithium-ion batteries to high temperatures and high voltages. This occurs due to transition metal dissolution from the high voltage spinel or layered oxide cathode material, ion migration through the electrolyte, and deposition on the solid-electrolyte interphase (SEI) on the anode. While much research has been done to track the oxidation state of the transition metal in the cathode material or deposited on the anode, there have been mixed reports on the chemical state of the transition metal ions dissolved in the electrolyte depending on the type of cathode used. X-ray absorption near edge spectroscopy (XANES) was performed on electrolytes extracted from full cells built with four different cathode materials that were cycled at either high or standard voltages to determine the chemical state of Mn and Ni in solution. Inductively coupled plasma-mass spectrometry (ICP-MS) was performed on the anodes from these cells to determine the concentration of deposited metal ions.

Stabilizing High-Voltage Lithium-Ion Battery Cathodes Using Functional Coatings of 2D Tungsten Diselenide

Functional surface coatings were applied on high voltage spinel (LiNi0.5Mn1.5O4; LNMO) and Ni-rich (LiNi0.85Co0.1Mn0.05O2; NCM851005) NCM cathode materials using few-layered 2H tungsten diselenide (WSe2). Simple liquid-phase mixing with WSe2 in 2-propanol and low-temperature (130 °C) heat treatment in nitrogen flow dramatically improved electrochemical performance, including stable cycling, high-rate performance, and lower voltage hysteresis in Li coin cells at 30 and 55 °C. Significantly improved capacity retention at 30 °C [Q401/Q9 of 99% vs 38% for LNMO and Q322/Q23 of 64% vs 46% for NCM851005] indicated efficient functionality. TEM and XPS clarified the coating distribution and coordination with the cathode surface, while postcycling studies revealed its sustainability, enabling lower transition metal dissolution and minor morphological deformation/microcrack formation. A modified and stable SEI was apparently formed owing to W and Se deposition on the Li anode during cycling. The synergistic functionalization provided a significant dual benefit of cathodic and anodic stability.

Identifying Element-Modulated Reactivity and Stability of the High-Voltage Spinel Cathode Materials via In Situ Time-Resolved X-Ray Diffraction.

Designing and identifying a dopant-involved material is quite significant, especially for battery science. LiNi0.5Mn1.5O4, being one of the most appealing candidates for high-potential lithium-ion batteries, has attracted immense attention and been investigated with Al or F dopants for its undesirable inherent structural challenges. Although the excellent performance of Al- or F-doped LiNi0.5Mn1.5O4 has been reported previously, the relationship between dopants, structural variation, and electrochemistry has not been fully identified. Hence, synchronous time-resolved XRD techniques are applied for identifying a guideline of the phase variations in cathodic (Al3+)- and anodic (F-)-substituted LiNi0.5Mn1.5O4, which revealed a three-phase evolution as a function of structural stability. Also, the Al-substituted materials exhibit excellent reactivity and stability, which can be clearly identified via the stable buffer phase existing in high power density or after long cycling due to the improvement in reaction kinetics of phase transition and the lithium-ion diffusion coefficient, just opposite to F doping. This provides a good guideline for identifying an element-modulated mechanism of reactivity or stability of materials science.

Composite Cathode for All Solid-State Lithium Batteries: A Gear up Towards Co-Sintering

The demand for energy storage systems has exponentially grown over the last decade. Li-ion battery, containing liquid electrolyte, is the most advanced and implemented technology for transport and stationary markets.[1] However, safety limitations of these systems mainly due to flammable and volatile electrolyte represent the major threat to reach complete market maturity.[2] Replacing liquid by safe solid electrolyte is foreseen as a realistic strategy while maintaining high energy and power densities.Among solid-state electrolyte materials, oxide-based ceramic electrolytes show high ionic conductivity, intrinsic safety and wide electrochemical window. The development of all-inorganic solid batteries is still at its infancy and presents various challenges due to the mechanical properties and processing of these materials.[3] High processing temperatures is certainly needed leading to chemical reactions and elemental diffusion, detrimental to maintain the battery performances.Developing a fully inorganic solid-state battery, consisting of a composite cathode, solid electrolyte and lithium metal anode by co-sintering the first two components, remains a great challenge. The composite cathode comprises the active material, and an ionic and an electronic conductive filler, that should form stable interfaces under processing as well as during cycling. But densification of oxide-based ceramic electrolytes requires temperatures as high as 1000 °C and co-sintering at these temperatures can induce numerous chemical side- reactions at composite cathode[4] which is detrimental to maintain the battery performance. To control the sintering process, the threshold temperature at which the material is stable and maintains the electrochemical performance needs to be defined and the reaction byproducts need to be identified to prevent and control their impact. In this work we will present the impact of heat treatment on the stability of composite cathode mixture with LiNi0.6Co0.2Mn0.2O2 (NMC), Li1+xAlxTi2-xP3O12 (LATP) and Ketjen black (KB). The study optimizes the threshold conditions such as heating atmosphere and temperature in determining the chemical and electrochemical compatibility of the composite and explains the reaction mechanism at threshold limits. Surface based analysis of the active material demonstrates that the NMC surface reconstruction acts as barrier to electrochemistry after heat treatment at temperatures above threshold limits. Also, it underlines the fact that each element of the composite has inevitable contribution to the reaction mechanism and is determined by both heating atmosphere and temperature. Alternatives to enhance the threshold limits will be proposed. Reference: [1] M. Armand and J. M. Tarascon, “Building better batteries,” Nature, vol. 451, no. 7179. Nature Publishing Group, pp. 652–657, 07-Feb-2008, doi: 10.1038/451652a.[2] D. Lisbona and T. Snee, “A review of hazards associated with primary lithium and lithium-ion batteries,” Process Saf. Environ. Prot., vol. 89, no. 6, pp. 434–442, Nov. 2011, doi: 10.1016/j.psep.2011.06.022.[3] K. Kerman, A. Luntz, V. Viswanathan, Y.-M. Chiang, and Z. Chen, “Review—Practical Challenges Hindering the Development of Solid State Li Ion Batteries,” J. Electrochem. Soc., vol. 164, no. 7, pp. A1731–A1744, Jun. 2017, doi: 10.1149/2.1571707jes.[4] L. Miara et al., “About the Compatibility between High Voltage Spinel Cathode Materials and Solid Oxide Electrolytes as a Function of Temperature,” vol. 8, no. 40, pp. 26842–26850, Oct. 2016, doi: 10.1021/acsami.6b09059.

Protective Spinel Coating for Li1.17Ni0.17Mn0.50Co0.17O2 Cathode for Li-Ion Batteries through Single-Source Precursor Approach.

The Li1.17Ni0.17Mn0.50Co0.17O2 Li-rich NMC positive electrode (cathode) for lithium-ion batteries has been coated with nanocrystals of the LiMn1.5Co0.5O4 high-voltage spinel cathode material. The coating was applied through a single-source precursor approach by a deposition of the molecular precursor LiMn1.5Co0.5(thd)5 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) dissolved in diethyl ether, followed by thermal decomposition at 400 °C inair resulting in a chemically homogeneous cubic spinel. The structure and chemical composition of the coatings, deposited on the model SiO2 spheres and Li-rich NMC crystallites, were analyzed using powder X-ray diffraction, electron diffraction, high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and energy-dispersive X-ray (EDX) mapping. The coated material containing 12 wt.% of spinel demonstrates a significantly improved first cycle Coulombic efficiency of 92% with a high first cycle discharge capacity of 290 mAhg−1. The coating also improves the capacity and voltage retention monitored over 25 galvanostatic charge–discharge cycles, although a complete suppression of the capacity and voltage fade is not achieved.

Understanding the impact of calcination time of high-voltage spinel Li1+xNi0.5Mn1.5O4 on structure and electrochemical behavior

The high-voltage spinel cathode material LiNi0.5Mn1.5O4 (LNMO) with its high energy per mass and volume is widely considered as promising alternative to the cobalt-containing state-of-the-art layered cathode materials. LNMO is usually charged/discharged at high voltage to make use of Ni-redox at the 4.7 V plateau, while after insertion of additional lithium the utilization of excess Li at the low voltage region of LNMO (<3.0 V) may compensate active lithium losses upon operation. Such a Li-excess stoichiometry of the spinel cathode can be achieved for instance through chemical pre-lithiation. Besides the compensation of Li losses, the additional Li also may also lead to an increase of the specific capacity. This study aims for a better understanding of the impact of the calcination time of LNMO particles on the low voltage region and an in-depth discussion of the results in the context of previous literature reports. Therefore, LNMO is synthesized by a ball-mill assisted solid-state synthesis and the calcination time is systematically changed. The subsequent structural and electrochemical analysis of the material shows for the first time that the material properties, including particle size and lattice parameter, as well as the charge/discharge current rate in general have a strong impact on the capacity ratio of the 2.7 V/2.1 V plateaus and that discharging (=lithiating) the cathode material to 1.5 V leads to irreversible changes within the material, which are however beneficial for its specific energy. Furthermore, the cathode material is cycled in the intermediate voltage range (2.4–4.95 V), demonstrating high specific capacities and excellent long-term stability over 100 cycles (≈179.5 ± 0.1 mAh g−1 and 96.4% ± 0.3%, respectively).

Electrochemical performance of Mo doped high voltage spinel cathode material for lithium-ion battery

This article deals with the properties of high-voltage cathode material LiNi0.5Mn1.5O4 synthesized by a solid-state reaction method and the influence of doping this material by molybdenum. The samples – LiMox + yNi0.5 - xMn1.5 - yO4 with different Mo contents (x = 0.00, 0.05, y = 0.00, 0.05) were successfully synthesized by two step annealing process and they were then investigated by SEM, EDS spectroscopy, thermo gravimetric analysis, cyclic voltammetry and charge–discharge tests at different loads and high temperature in lithium-ion cells with metal lithium as a counter electrode. Results showed that the initial discharge capacity and capacity during high temperature cycling of the LiMox + yNi0.5 - xMn1.5 - yO4 cathode were improved with addition of Mo when x = 0.05. Thermal analysis results suggested that the Mo doping slightly improved the stability of the crystal structure of the LiNi0.5Mn1.5O4 cathode which leads to an improved stability during high temperature galvanostatic cycling.

Tuning Electrochemical Performance through Non-stoichiometric Compositions in High-voltage Spinel Cathode Materials

Tuning Electrochemical Performance through Non-stoichiometric Compositions in High-voltage Spinel Cathode Materials

Influence of Conditions on the Process of Spinel Based Cathode Material Synthesis

For advanced applications, such as electric vehicles, it is necessary to achieve high battery pack voltage reaching hundreds of volts and high capacity at the same time. These requirements should be met by new accumulators based on high-voltage cathode materials with their voltage close to 5 V rather than by currently used Li-Ion accumulators. Due to higher working voltages of these materials, the number of cells required to achieve the desired voltage is lower, thereby the battery pack is smaller and lighter. For good operation of these materials, their synthesis must be accurate. This paper deals with the influence of used gas in the oven chamber during the synthesis of high voltage spinel cathode material LiNi0.5Mn1.5O4. Final materials were studied using scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS). Crystalline structure was studied by X-ray diffraction (XRD). Subsequently, electrochemical properties of these electrode materials were also tested by electrochemical methods.

Kinetic Study of High Voltage Spinel Cathode Material in a Wide Temperature Range for Lithium Ion Battery

This study represents the electrochemical performance and lithium transportation behaviors of spinel LiNi0.5Mn1.5O4 cathode operated in a wide range of temperatures from −20 to 60°C. The correlative lithium diffusion coefficients are derived via electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques, respectively. Based on the modeling of EIS, the lithium diffusivity of LiNi0.5Mn1.5O4 is estimated in the range of 10−11 around 25°C. The specific capacity of LiNi0.5Mn1.5O4 cathode is highly associated with the change of Li-ion mobility, which reveals a distinctive trend with applied temperatures. A strong correlation is also found between the apparent activation energy and lithium diffusivity. The change of activation energy is a key factor in dominating the kinetic reaction of Li/LiNi0.5Mn1.5O4 cells. Furthermore, the voltage polarization recorded from CV profile also perfectly follows the lithium transportation scenario. This study elaborates a profound discussion for temperature effects on electrochemical properties of LiNi0.5Mn1.5O4 cathode material.

Designed seamless outer surface: Application for high voltage LiNi0.5Mn1.5O4 cathode with excellent cycling stability

Suppressing side reactions at the cathode-electrolyte interface (CEI) is critical for alleviating capacity fading of the high-voltage (>5 V) spinel cathode material LiNi0.5Mn1.5O4 (LNMO). The primary bottleneck in conventional nanoengineering of LNMO involves an antagonistic relationship between the positive effects of the nanometer particle size and negative effects stemming from the larger CEI area. Inspired by Buckminster Fuller's geodesic domes, we have designed a seamless LNMO hollow sphere (S-LNMO) that comprises average 120 nm-sized triangles and truncated triangle subunits by means of grain growth orientation. The “tensegrity” structure has efficiently hindered the interfacial side reaction, which occurs only within a depth of 5 nm from the surface, thereby improving its electrochemical stability. The embedded layered Li2TiO3 (LTO) in bulk S-LNMO (LTO:S-LNMO) region further improved the high-rate performance, demonstrating an ∼110 mAh/g capacity with 80.9% retention after 400 cycles at 5 C and remaining stable after 900 cycles at 5 C even after being stored at 50 °C for one week.

About the Compatibility between High Voltage Spinel Cathode Materials and Solid Oxide Electrolytes as a Function of Temperature.

The reactivity of mixtures of high voltage spinel cathode materials Li2NiMn3O8, Li2FeMn3O8, and LiCoMnO4 cosintered with Li1.5Al0.5Ti1.5(PO4)3 and Li6.6La3Zr1.6Ta0.4O12 electrolytes is studied by thermal analysis using X-ray-diffraction and differential thermoanalysis and thermogravimetry coupled with mass spectrometry. The results are compared with predicted decomposition reactions from first-principles calculations. Decomposition of the mixtures begins at 600 °C, significantly lower than the decomposition temperature of any component, especially the electrolytes. For the cathode + Li6.6La3Zr1.6Ta0.4O12 mixtures, lithium and oxygen from the electrolyte react with the cathodes to form highly stable Li2MnO3 and then decompose to form stable and often insulating phases such as La2Zr2O7, La2O3, La3TaO7, TiO2, and LaMnO3 which are likely to increase the interfacial impedance of a cathode composite. The decomposition reactions are identified with high fidelity by first-principles calculations. For the cathode + Li1.5Al0.5Ti1.5(PO4)3 mixtures, the Mn tends to oxidize to MnO2 or Mn2O3, supplying lithium to the electrolyte for the formation of Li3PO4 and metal phosphates such as AlPO4 and LiMPO4 (M = Mn, Ni). The results indicate that high temperature cosintering to form dense cathode composites between spinel cathodes and oxide electrolytes will produce high impedance interfacial products, complicating solid state battery manufacturing.

NaMn2-xNixO4 Derived from Mesoporous LiMn2-xNixO4: High-Voltage Spinel Cathode Materials for Na-Ion Batteries

Sodium ion batteries are a topic of emerging interest, as the low cost and high natural abundance of sodium precursors provide a specific advantage over commercial lithium ion batteries. Comparatively, sodium chemistries suffer from lower operating voltages, making the development of suitable high voltage positive electrodes key to enabling sodium chemistries capable of direct replacement for modern lithium ion storage devices. Herein, we investigate dis/ordered nickel doped manganese spinels (NaxMn2-yNiyO4) as a positive electrode for sodium ion battery applications. Due to the kinetic limitations of the sodium de/insertion reaction into Na1-xMn2-yNiyO4 the effect of both temperature and the electrochemical cycling window are studied revealing a unique reaction pathway and potential optimization routes for further study.

A facile approach to derive binder protective film on high voltage spinel cathode materials against high temperature degradation

The electrochemical performance of spinel LiNi0.5Mn1.5O4 cathode combined with different binders at elevated temperature is firstly investigated. The water soluble binder, such as sodium carboxymethyl cellulose (CMC) and sodium alginate (SA), is compared with the polyvinylidene difluoride (PVdF) binder used in non-aqueous process. The aqueous process can meet the need of Li-ion battery industry due to environmental-friendly and cost effectiveness by replacing toxic organic solvent, such as N-methyl-pyrrolidone (NMP). In this study, a significantly improved high temperature cycling performance is successfully obtained as compared to the traditional PVdF binder. The aqueous binder can serve as a protective film which inhibits the serious Ni and Mn dissolution especially at elevated temperature. Our result demonstrates a facile approach to solve the problem of capacity fading for high voltage spinel cathodes.

(Invited) Effects of Crystalline Structure on the Electrochemical Properties of High Voltage Spinel Cathode Materials

LiNi0.5Mn1.5O4 powders were prepared via a spraying-dry method followed by heating at temperatures between 600 and 1000oC for 8 hours in air with oven cooling. In order to eliminate the particle size effects, 900oC samples were annealed at 700oC under air for various durations. The crystalline structure of the prepared samples were investigated from their high resolution neutron powder diffraction data collected with Echidna at ANSTO and refined with Rietica Ver. 1.77. The results of Rietveld refinement for the NPD patterns manifest that the 700oC prepared sample contains 85% of ordered P4332 and 15% of disordered Fd m phases whereas the powders prepared at temperatures higher than 800oC prevailed with disordered Fd m phase (72`75%) with amount of rock-salt LixNi1-xO increases from 1 to 4% with heating temperature. For the annealed samples, the molar fraction of the ordered phase increases with increasing duration of annealing and converts completely into ordered phase after annealing for 60 hours. It suggests that the phase conversion and LixNi1-xO evolution/dissolution are reversible [1]. From the results of capacity retention study of the cells comprised with the prepared powders, it was found that sample prepared at 900oC with oven cooling exhibits the most promising performance among the prepared powders. These results are different from those reported by Fang et al. [2], however, they are similar to those reported previously that the disordered phase has better electrochemical properties than the ordered phase [3-5]. Though various reasons had been suggested [3, 6-7], the effects of crystalline structure on the cycling performance of high voltage spinel are still not clear. In this study, the effects are hope to reveal from the results of dissolution study for transition metals upon storage and cycling, linear sweep voltammetry for electrolyte oxidation on high voltage spinel, cyclic voltammetry for Li+ ion diffusivity, and the phase evolution detected by high resolution TEM for the fresh and cycled electrodes and in-situ NPD study. Reference: [1] L. Cai, Z. Liu, K. An, and C. Liang, J. Mater. Chem. A, 1,6908 (2013). [2] H. Fang, Z. Wang, B. Zhang, X. Li and G. Li, Electrochem. Commun., 9, 1077 (2007). [3] J. H. Kim, S. T. Myung, C. S. Yoon, S. G. Kang and Y. K. Sun, Chem. Mater., 16, 906 (2004). [4] A. Bhaskar, N. N. Bramnik, A. Senyshyn, H. Fuess and H. Ehrenberg, J. Electrochem. Soc., 157, A689 (2010). [5] K. Takahashi, M. Saitoh, M. Sano, M. Fujita and K. Kifune, J. Electrochem. Soc., 151, A173 (2004). [6] M. Kunduraci, J. F. Al-Sharab and G. G. Amatucci, Chem. Mater., 18, 3585 (2006). [7] X. H. Ma, B. Kang and G. Ceder, J. Electrochem. Soc., 157, (2010).

High-Performance LiNi0.2Mn1.8O4 Spinel Cathode Material for Lithium Ion Batteries Obtained By Microwave-Assisted Synthesis

High energy density rechargeable lithium ion batteries are considered as more efficient energy storage devices for use from portable consumer electronics to large-scale applications. Apparently, the high voltage spinel and olivine lithium iron phosphate cathode materials are being considered as the target materials to achieve sustainable development, particularly for large-scale utility with energetic (energy and power density) and economic aspects. Obviously, the spinel materials are abruptly beginning to attract owing to its high electrochemical performance at room temperature. Unfortunately, the above material remains inferior due to its large capacity loss observed when operating at higher temperature. Obviously, the spinel, LiNi0.5Mn1.5O4 with a potential plateau of~4.7V is abruptly beginning to attract owing to its high electrochemical performance at room temperature. Unfortunately, the specific composition of above material remains inferior due to its high operation potential which cause the electrolyte oxidation, especially a large capacity loss observed when operating at higher temperature [1, 2]. Considering the above aspects, the commercial lithium manganese oxide spinel, LiMn2O4 (LMO) cathode can become preferable candidate particularly with regard to costs, environmental and efficiency perspectives. However, the LMO also suffer from the rapid capacity fading with cycling due to the manganese dissolution at an elevated temperature which limits the practical use of this material for large-scale applications. Numerous efforts have been proposed to overcome this issue. Recently, researchers demonstrated the excellent performance of octahedral LMO and attributed it to their surface facets, especially {111} which allow for thinner SEI formation than {110} facets [3, 4]. LMO chemistry can be improved by doping with very small amount of the nickel, e.g., LiNi0.2Mn1.8O4 [5]. As part our continuing investigations on the impact of microwave chemistry on the electrochemical performance of battery materials [6], we report the preparation of nickel-doped LMO (i.e., LiNi0.2Mn1.8O4) with microwave irradiation as an essential step to achieve enhanced electrochemistry. As-prepared active Mn3O4 with well-shaped octahedral {011} facets morphology was doped with lithium and very low amount of Ni to give LiNi0.2Mn1.8O4 spinel with exposed {111} facets (Fig.1a) that allowed for structural and cycle stability. In addition, the 6,7Li MAS NMR shows the two isotropic Li resonance of nearly 528.4 - 604.7 ppm and 528-596.3 ppm for LMNO and LMNO-mic results the multiple Li environments by the distribution of Mn and Ni atoms. Interestingly, the microwave irradiated spinel delivered a better cycle stability, rate capability, low impedance, and improved lithium diffusivity at different temperatures compared to the untreated one. In this presentation, we will discuss in detail our findings on the impact of microwave irradiation on the electrochemical performance of the LiNi0.2Mn1.8O4 spinel at ambient and high temperature (60oC). Fig.1: (a) SEM image of LMNO-mic with {111} facets, and (b) Cycle stability of LMNO and LMNO-mic at 60oC References 1) O. K. Park, Y. Cho, S. Lee, H. C. Yoo, H. K. Song, J. Cho, Energy Environ. Sci. 2011, 4, 1621-1633. 2) S. T. Myung, K. S. Lee, D. W. Kim, B. Scrosati, Y. K. Sun, Energy Environ. Sci. 2011, 4, 935-939. 3) K. R. Chemelewski, E. S. Lee, W. Li, A. Manthiram, Chem. Mater. 2013, 25, 2890-2897. 4) B. Hai, A. K. Shukla, H. Duncan, G. Chen, J. Mater. Chem. A, 2013, 1, 759-769 5) M.A. Kebede, N. Kunjuzwa, C.J. Jafta, M.K. Mathe, K.I. Ozoemena, Electrochim. Acta 2014, 128, 172 - 177 6) C.J. Jafta , M. K. Mathe , N. Manyala , W.D. Roos, K.I. Ozoemena, ACS Appl. Mater. Interfaces, 2013, 5, 7592−7598 Figure 1

Study of electrochemical properties and thermal stability of the high-voltage spinel cathode material for lithium-ion accumulators

This article deals with the properties of high-voltage cathode material LiNi0.5Mn1.5O4 synthesised by a solid-state reactions method. The sample—LiNi0.5Mn1.5O4—was synthesised by two steps of annealing process. A number of electrochemical and physical methods were used to analyse the samples. The obtained LiNi0.5Mn1.5O4 powder was characterised by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and galvanostatic charge/discharge measurements at different loads and high temperature in lithium-ion cells with metal lithium as a counter electrode. All these analyses were used for confirmation of the structure of the material LiNi0.5Mn1.5O4 and for investigating its electrochemical properties. A special analysis was used for this paper to understand and confirm the function of this type of material. It is called electron paramagnetic resonance (EPR) spectroscopy, which is used in the field of lithium-ion batteries and also which is not common. This analysis is typically used to analyse free radicals. It is possible to study changes of valence in cathode materials during charging and confirming the valence change of Mn from Mn3+ to Mn4+ and of Ni from Ni2+ to Ni3+ and then to Ni4+ with EPR analysis. Thermogravimetric (TG) analysis of stability of the material LiNi0.5Mn1.5O4 with in situ observation of structural changes by SEM was used as the last analysis.

Design and preparation of spherical high voltage LiNi0.5Mn1.5O4 with a novel concentration-gradient shell for lithium ion batteries

A core–shell structure high voltage spinel cathode material with an average composition of LiMg0.056Ni0.444Mn1.5O4 is firstly designed and synthesized via co-precipitation process. The spherical LiNi0.5Mn1.5O4 core material is encapsulated by a novel thin concentration-gradient shell (CGS) which decreases Ni concentration and increases Mg concentration toward the particle surface, and the composition of the outmost layer of the spherical LiMg0.056Ni0.444Mn1.5O4 is LiMg0.5Mn1.5O4. The electrochemical properties of the LiMg0.056Ni0.444Mn1.5O4 are carefully investigated and compared with the LiNi0.5Mn1.5O4 by electrochemical measurements. It has been found that the electrochemical properties of the LiMg0.056Ni0.444Mn1.5O4 sample are far superior to those of the LiNi0.5Mn1.5O4 sample. The LiMg0.056Ni0.444Mn1.5O4 sample exhibits excellent cycling performance. At 25 °C, it delivers a discharge capacity of 127 mAh g−1 between 3.0 and 4.9 V vs. Li/Li+ with a retention of 98.9% over 200 cycles at a rate of 1C (147 mA g−1). At 55 °C, it delivers a discharge capacity of 128 mAh g−1 with a retention of 99% after 100 cycles in the same charge–discharge condition. Besides, the LiMg0.056Ni0.444Mn1.5O4 shows a good rate capability, it can still deliver a high discharge capacity of 116 mAh g−1 even at a rate of 10C. Therefore, the core–shell structure high voltage spinel cathode material with CGS will be a promising cathode material for advanced lithium ion batteries.

Comparative Study of the Properties of High Voltage Spinel Cathode Material Depending on the Method of Synthesis

The most widely used cathode materials for lithium-ion accumulators nowadays are based on LiCoO2, LiFePO4 or LiMnO4. These materials are supposed to be replaced by battery systems with new generation of cathode materials such as sulphur-based or high-voltage cathode materials in the future. This article is focused on the study of electrochemical properties of high voltage cathode material LiCr0.1Ni0.4Mn1.5O4 depending on the process of synthesis. The samples were prepared by solid state reaction method with the temperature as an independent variable where electrochemical charge/discharge capacity retention was observed during cycling and also during cycling at different C rate. The structure and thermal stability of the particles of the synthesized materials was also studied by SEM and TGA.