Recent developments in the doping of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode material for 5 V lithium-ion batteries

LiMn₂O₄ has been considered a promising cathode material for lithium-ion batteries in electric vehicles. However, there are still a number of problems of severe capacity fading before any materials modifications. Among all doped LiMn₂O₄, spinel LiNi_0.5Mn_1.5O₄ material is seen as a potential cathode material for use in electric vehicles and energy storage systems in the future because of its high working potential (4.7 V), high energy density (the energy density of LiNi_0.5Mn_1.5O₄ is 20% higher than that of LiCoO₂), acceptable stability, and good cycling performance. In the presented paper, the structure and electrochemical performance of doped LiNi_0.5Mn_1.5O₄ are reviewed. The rate capability, rate performance and cyclic life of various doped LiNi_0.5Mn_1.5O₄ materials are described. This review also focuses on the present status of doped LiNi_0.5Mn_1.5O₄, then on its near future developments.     

Recent progress in the electrolytes for improving the cycling stability of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> high-voltage cathode

High-voltage spinel LiNi_0.5Mn_1.5O₄ has been considered one of the most promising cathode materials for lithium-ion power batteries used in electrical vehicles (EVs) or hybrid electrical vehicles (HEVs) because the high voltage plateau at around 4.7 V makes its energy density (658 Wh kg^?1) 30 and 25 % higher than that of conventional pristine spinel LiMn₂O₄ (440 Wh kg^?1) or olivine LiFePO₄ (500 Wh kg^?1) materials, respectively. Unfortunately, LiNi_0.5Mn_1.5O₄-based batteries with LiPF₆-based carbonate electrolytes always suffer from severe capacity deterioration and poor thermostability because of the oxidization of organic carbonate solvents and decomposition of LiPF₆, especially at elevated temperatures and water-containing environment. The major goal of this review is to highlight the recent advancements in the development of advanced electrolytes for improving the cycling stability and rate capacity of LiNi_0.5Mn_1.5O₄-based batteries. Finally, an insight into the future research and further development of advanced electrolytes for LiNi_0.5Mn_1.5O₄-based batteries is discussed.     

Nanosized LiNi0.5Mn1.5O4 spinels synthesized by a high-oxidation-state manganese sol–gel method

Nanosized LiNi_0.5Mn_1.5O₄ spinels with the uniform average particle size of about 80–100 nm were synthesized by a high-oxidation-state manganese sol–gel method. It indicates that the resulting nanosized LiNi_0.5Mn_1.5O₄ materials not only have a phase-pure cubic spinel structure without any impurity but also have a good dispersion even without any physical treatment. Besides, the cell based upon the resulting nanosized LiNi_0.5Mn_1.5O₄ materials shows good cycle stability and ratio performance. It suggests that the novel method would be helpful for the synthesis and application of LiNi_0.5Mn_1.5O₄ cathode.     

Recent advances on Fe- and Mn-based cathode materials for lithium and sodium ion batteries

The ever-growing market of electrochemical energy storage impels the advances on cost-effective and environmentally friendly battery chemistries. Lithium-ion batteries (LIBs) are currently the most critical energy storage devices for a variety of applications, while sodium-ion batteries (SIBs) are expected to complement LIBs in large-scale applications. In respect to their constituent components, the cathode part is the most significant sector regarding weight fraction and cost. Therefore, the development of cathode materials based on Earth’s abundant elements (Fe and Mn) largely determines the prospects of the batteries. Herein, we offer a comprehensive review of the up-to-date advances on Fe- and Mn-based cathode materials for LIBs and SIBs, highlighting some promising candidates, such as Li- and Mn-rich layered oxides, LiNi_0.5Mn_1.5O₄, LiFe_1-xMn_xPO₄, Na_xFe_yMn_1-yO₂, Na₄MnFe₂(PO₄)(P₂O₇), and Prussian blue analogs. Also, challenges and prospects are discussed to direct the possible development of cost-effective and high-performance cathode materials for future rechargeable batteries.     

AlF<Subscript>3</Subscript> coating of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> for high-performance Li-ion batteries

AlF₃-coating is attempted to improve the performance of LiNi_0.5Mn_1.5O₄ cathode materials for Li-ion batteries. The prepared powders are characterized by scanning electron microscope, powder X-ray diffraction, charge/discharge, and impedance. The coated LiNi_0.5Mn_1.5O₄ samples show higher discharge capacity, better rate capability, and higher capacity retention than the uncoated samples. Among the coated samples, 1.0 mol% AlF₃-coated sample shows highest capacity after charge–discharged at 30 mA/g for 3 cycles, but 4.0 mol% coated sample exhibits the highest capacity and cycling stability when cycled at high rate of 150 and 300 mA/g. The 40th cycle discharge capacity at 300 mA/g current still remains 114.8 mAh/g for 4.0 mol% AlF₃-coated LiNi_0.5Mn_1.5O₄, while only 84.3 mAh/g for the uncoated sample.     

Simple co-precipitation synthesis of high-voltage spinel cathodes with different Ni/Mn ratios for lithium-ion batteries

The high-voltage spinel is a promising cathode material in next generation of lithium-ion batteries. Samples LiNi_0.5???xMn_1.5?+?xO₄ (x?=?0, 0.05, 0.1) are synthesized by a simple co-precipitation method, in which pH value and temperature conditions do not need control. In the simple co-precipitation method, NaHCO₃ solution is poured into transition metal solution to produce precursor. Ni and Mn are distributed uniformly in the products. The as-prepared samples are composed of ~?200 nm primary particles. Samples LiNi_0.5???xMn_1.5?+?xO₄ (x?=?0, 0.05, 0.1) are also tested to study the effects of different Ni/Mn ratios. Sample LiNi_0.5Mn_1.5O₄ delivers discharge capacities of 130 mAh g^?1 at 0.2 C. The decreasing of Ni/Mn ratio in samples reduces specific capacity. With the decreasing of Ni/Mn ratios in spinel, amount of Mn³⁺ are increased. Attributed to its high Mn³⁺ contents, sample LiNi_0.4Mn_1.6O₄ delivers the highest discharge capacity of 106 mAh g^?1 at a large current density of 15 C, keeping 84.5% of that at 0.2 C rate. With the increasing of Ni/Mn ratios in spinel, cycling performance is improved. Sample LiNi_0.5Mn_1.5O₄ shows the best cycling stability, keeping 94.4% and 90.4% of the highest discharge capacities after 500 cycles at 1 C and 1000 cycles at 5 C.     

Sonochemical synthesis of LiNi0.5Mn1.5O4 and its electrochemical performance as a cathode material for 5 V Li-ion batteries

LiNi_0.5Mn_1.5O₄ was synthesized as a cathode material for Li-ion batteries by a sonochemical reaction followed by annealing, and was characterized by XRD, SEM, HRTEM and Raman spectroscopy in conjunction with electrochemical measurements. Two samples were prepared by a sonochemical process, one without using glucose (sample-S1) and another with glucose (sample-S2). An initial discharge specific capacity of 130 mA h g⁻¹ is obtained for LiNi_0.5Mn_1.5O₄ at a relatively slow rate of C/10 in galvanostatic charge–discharge cycling. The capacity retention upon 50 cycles at this rate was around 95.4% and 98.9% for sample-S1 and sample-S2, respectively, at 30 °C.     

Optimal concentration of electrolyte additive for cyclic stability improvement of high-voltage cathode of lithium-ion battery

Additives that can be oxidized preferentially to the baseline electrolyte are possible of forming a protective cathode interphase, but less attention has been paid to the effect of the additive concentration. Herein, this issue is addressed by evaluating the effect of an easily oxidizable electrolyte additive, tripropyl borate (TPB), on the cyclic stability of high-voltage cathode, LiNi_0.5Mn_1.5O₄. It is found that the optimal concentration of TPB is 1 wt.% for the best cyclic stability of LiNi_0.5Mn_1.5O₄ and the discharge capacity of LiNi_0.5Mn_1.5O₄ will decrease when TPB concentration is lower or higher than this concentration. This effect is related to the resulting interphase from TPB, which cannot provide sufficient protection for the structural integrity of LiNi_0.5Mn_1.5O₄ when it is formed in the electrolyte with lower concentrations of TPB, while shows an increased interfacial impedance of LiNi_0.5Mn_1.5O₄/electrolyte when it is formed from higher concentrations of TPB.     

Synthesis of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> nano/microspheres with adjustable hollow structures for lithium-ion battery

High-voltage spinel LiNi_0.5Mn_1.5O₄ nano/microspheres with adjustable hollow structures have been fabricated based on the Kirkendall effect. The main characteristic is that the wall thickness of the hollow structure as well as the cavity size of the hollow structure can be adjusted by the different ratio of mixed precipitation agents. Especially, the diagrammatic sketch for the formation process of various LiNi_0.5Mn_1.5O₄ materials with adjustable hollow structures is discussed. Besides, the results of electrochemical performance test show that LiNi_0.5Mn_1.5O₄ obtained from 10:1 Na₂CO₃/NaOH (in mole) ratio is worth looking forward to, owing to its special hierarchical nano/microsphere and moderate hollow structures.     

Preparation of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode materials by electrospinning

LiNi_0.5Mn_1.5O₄ cathode material was prepared by electrospinning using lithium hydroxide, manganese acetate, nickel acetate, acetic acid, ethanol, and poly(vinyl pyrrolidone) as raw materials. The effect of calcination temperature on the structure, morphology, and electrochemical properties was investigated. XRD results indicate that the LiNi_0.5Mn_1.5O₄ composite is well crystallized as a spinel structure at calcination temperature of 650 °C for 3 h. SEM results reveal that this composite has a nanofiber shape with average size of about 300–500 nm. Electrochemical performance tests reveal that this composite shows the initial discharge capacity of 127.8 and 105 mAhg^?1 at 0.1 and 3 C rates, respectively, and exhibits good cycling performance.     

Effects of lithium excess amount on the microstructure and electrochemical properties of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode material

Spinel LiNi_0.5Mn_1.5O₄ cathode materials with different lithium excess amount (0, 2%, 6%, 10%) were synthesized by a facile solid-state method. The effect of lithium excess amount on the microstructure, morphology, and electrochemical properties of LiNi_0.5Mn_1.5O₄ materials was systematically investigated. The results show that the lithium excess amount does not change the particle morphology and size obviously; thus, the electrochemical properties of LiNi_0.5Mn_1.5O₄ are mainly determined by structural characteristics. With the increase of lithium excess amount, the cation disordering degree (Mn³⁺ content) and phase purity first increase and then decrease, while the cation mixing extent has the opposite trend. Among them, the LiNi_0.5Mn_1.5O₄ material with 6% lithium excess amount exhibits higher disordering degree and lower impurity content and cation mixing extent, thus leading to the optimum electrochemical properties, with discharge capacities of 125.0, 126.1, 124.2, and 118.9 mAh/g at 0.2-, 1-, 5-, and 10-C rates and capacity retention rate of 96.49% after 100 cycles at 1-C rate.     

Structure and insertion properties of disordered and ordered LiNi0.5Mn1.5O4 spinels prepared by wet chemistry

We present the synthesis, characterization, and electrode behavior of LiNi_0.5Mn_1.5O₄ spinels prepared by the wet-chemical method via citrate precursors. The phase evolution was studied as a function of nickel substitution and upon intercalation and deintercalation of Li ions. Characterization methods include X-ray diffraction, SEM, Raman, Fourier transform infrared, superconducting quantum interference device, and electron spin resonance. The crystal chemistry of LiNi_0.5Mn_1.5O₄ appears to be strongly dependent on the growth conditions. Both normal-like cubic spinel [Fd3m space group (SG)] and ordered spinel (P4 ₁ 32 SG) structures have been formed using different synthesis routes. Raman scattering and infrared features indicate that the vibrational mode frequencies and relative intensities of the bands are sensitive to the covalency of the (Ni, Mn)-O bonds. Scanning electron microscopy (SEM) micrographs show that the particle size of the LiNi_0.5Mn_1.5O₄ powders ranges in the submicronic domain with a narrow grain-size distribution. The substitution of the 3d⁸ metal for Mn in LiNi_0.5Mn_1.5O₄ oxides is beneficial for its charge–discharge cycling performance. For a cut-off voltage of 3.5–4.9 V, the electrochemical capacity of the Li//LiNi_0.5Mn_1.5O₄ cell is ca. 133 mAh/g during the first discharge. Differences and similarities between LiMn₂O₄ and LiNi_0.5Mn_1.5O₄ oxides are discussed.     

Study on the electrochemical performance of LiNi0.5Mn1.5O4 with different precursor

LiNi_0.5Mn_1.5O₄ cathodes were synthesized by three different raw materials at high temperature. The samples were characterized by X-ray diffraction and scanning electron microscopy tests, respectively. The results indicate that the synthesized samples show pure spinel structure, and the samples synthesized by nickel?Cmanganese hydrate and nickel?Cmanganese oxide show regular geometrical shape. The electrochemical performance of sample synthesized by nickel?Cmanganese oxide is best. The first discharge capacity is 141 mAh/g, and the capacity retention is 98.6% after 50 cycles at 0.5?C rate. The discharge capacity at 5?C rate is still 120 mAh/g. Better crystallization, smaller specific surface area, and lower polarization may be responsible for the excellent electrochemical performance of the LiNi_0.5Mn_1.5O₄.     

Structural and magnetic properties of LiNi0.5Mn1.5O4 and LiNi0.5Mn1.5O4-δ spinels： A first-principles study

<正>Structural and magnetic properties of LiNi_0.5Mn_1.5O₄ and LiNi_0.5Mn_1.5O_4-δ are investigated using densityfunctional theory calculations.Results indicate that nonstoichiometric LiNi_0.5Mn_1.5O_4-δ and stoichiometric LiNi_0.5Mn_1.5O₄ exhibit two different structures,i.e.,the face-centred cubic（Fd-3m） and primitive,or simple,cubic （P4₃32） space groups,respectively.It is found that the magnetic ground state of LiNi_0.5Mn_1.5O₄（P4₃32 and Fd-3m） is a ferrimagnetic state in which the Ni and Mn sublattices are ferromagnetically ordered along the[110]direction whereas they are antiferromagnetic with respect to each other.We demonstrate that it is the presence of an O-vacancy in LiNi_0.5Mn_1.5O_4-δ with the Fd-3m space group that results in its superior electronic conductivity compared with LiNi_0.5Mn_1.5O₄ with the P4₃32 space group.     

Flame synthesis of 5 V spinel-LiNi0.5Mn1.5O4 cathode-materials for lithium-ion rechargeable-batteries

The lithium transition metal oxide LiNi_0.5Mn_1.5O₄ with an space group (SG) structure has shown great potential as a cathode material for 5 V lithium-ion rechargeable-batteries. In this work, a flame-assisted spray technology (FAST) was developed to produce nanostructured LiNi_0.5Mn_1.5O₄ powder in a continuous manner. The as-synthesized powder had a uniform morphology, was spherical in shape and had a nanocrystalline structure, as observed by SEM and TEM. The XRD pattern of the as-synthesized powder matched the spectrum of spinel-LiNi_0.5Mn_1.5O₄. The average grain size was about 16 nm, as calculated by XRD. However, XRD also indicated the impurity Mn₂NiO₄ in the powder. By varying flame temperature, it was possible to show that the impurity was formed due to the high temperature of the flame. While flame temperature was minimized by lowering the H₂/N₂ ratio, it was not possible to completely eliminate Mn₂NiO₄ from the as-synthesized powder. After annealing at 800 °C for 2 h, the impurity was eliminated, and the XRD pattern of the powder indicated a pure-phase spinel structure with an SG. The electrochemical performance of the flame-synthesized LiNi_0.5Mn_1.5O₄ powder was tested in coin-type test batteries that were charged and discharged at constant current under a 5 V potential. The test cells showed the characteristic voltage plateaus of spinel-LiNi_0.5Mn_1.5O₄ ( SG). The material proved to be electrochemically active as a cathode material for lithium-ion rechargeable-batteries.     

Synthesis and characterization of spinel type high-power cathode materials Li MxMn2−x O4 (M=Ni,Co, Cr)

The transition metal-doped spinel cathode materials, LiM_0.5Mn_1.5O₄ (M=Ni. Co, Cr) were prepared by solid-state reaction. The structure and morphology of the samples were investigated by X-ray diffraction, Rietveld refinement and scanning electron microscopy (SEM). The diffraction peaks of all the samples corresponded to a single phase of cubic spinel structure with a space group Fd3m. Field-emission SEM shows octahedron like shapes and the primary particles size was between 500 nm and 2 μm. Oxidation states of Ni, Co and Cr were found to be 2+, 2+ and 3+ as revealed by X-ray photoelectron spectroscopy. During discharging, LiNi_0.5Mn_1.5O₄ and LiCo_0.5Mn_1.5O₄ sample shows more than 130 mAh/g between 3.5 and 5.2 V at a current density of 0.65 mA/cm² and well developed plateau around 5 V, respectively.     

Understanding the thermal stability and bonding characteristic of Li<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> as cathode materials for lithium-ion battery from first principles

The thermodynamic stability is a very important quantity for the electrode materials, because it is not only related to the electrochemical performances of the materials but also the safety issue of the cells. To evaluate the thermodynamic stability of Li _x Ni_0.5Mn_1.5O₄ (x = 0, 1), the formation enthalpies from elemental phases and oxides were obtained. The values for LiNi_0.5Mn_1.5O₄ were calculated to be ?1341.10 and ?141.84 kJ mol^?1, while those for Ni_0.5Mn_1.5O₄ were ?949.11 and ?49.21 kJ mol^?1. These values are much more negative than those of LiCoO₂ and LiNiO₂ compounds, indicating that the thermodynamic stability of Li _x Ni_0.5Mn_1.5O₄ is better than the two classic compounds. To clarify the microscopic origin, the density of states, magnetic moments, and bond orders were systematically investigated. The results showed that the excellent thermodynamic stability of LiNi_0.5Mn_1.5O₄ is attributed to the absence of Jahn-Teller distortions, strong electrostatic interactions of Li–O ionic bond, and strong Ni–O/Mn–O ionic-covalent mixing bonds. After lithium extraction, the disappearance of the pure Li–O bonds leads to an increase of formation enthalpy, indicating a decreasing thermodynamic stability for Ni_0.5Mn_1.5O₄ with respect to LiNi_0.5Mn_1.5O₄.     

Spinel-type solid solutions involving Mn and Ti:Crystal chemistry, magnetic and electrochemical properties

This study reports the structural and magnetic properties of spinel systems Li₄Mn_5−xTi_xO₁₂ (“4-5-12” series) and LiNi_0.5Mn_1.5−xTi_xO₄ (“LNMTO” series), both based on Mn⁴⁺ substitution by Ti⁴⁺. Intermediate compositions covering the whole range of compositions (0≤x≤5 and 0≤x≤1.5, respectively) were prepared by solid state reaction. The 4-5-12 system forms a continuous spinel solid solution, whereas the spinel phase range in LNMTO stops before the end member “LiNi_0.5Ti_1.5O₄”, which is multi-phased with a major hexagonal phase component. Cell parameters and (Mn,Ti)-O distances increase monotonically with titanium content in both series. In the LNMTO series, the end member LiNi_0.5Mn_1.5O₄ is known to form a superstructure with Ni/Mn cation ordering. Neutron diffraction and Raman spectroscopy show that this order is lost when Ti is substituted, even at low level (x=0.15). The LNMTO crystal chemistry is also complicated by the presence of partial cation inversion, and the presence of a secondary rocksalt-type phase that modifies the spinel stoichiometry. Magnetic properties are characterized by a competition between ferromagnetic and antiferromagnetic interactions; no magnetic ordering is achieved, in agreement with B-site cation frustration and disorder. Electrochemical measurements show that the Ti^3+/4+ and Mn^3+/4+ redox couples behave independently in the 4-5-12 series, and that titanium decreases the high-potential electrochemical redox activity of LNMTO because of its blocking character for electron transfer to and from the nickel sites in the spinel structure.     

LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> hollow nano-micro hierarchical microspheres as advanced cathode for lithium ion batteries

The high-voltage spinel-type LiNi_0.5Mn_1.5O₄ (LNMO) is a promising cathode material for next-generation lithium ion batteries. In this study, hollow LNMO microspheres have been synthesized via co-precipitation method accompanied with high-temperature calcinations. The physical and electrochemical properties of the materials are characterized by x-ray diffraction (XRD), TGA, RAMAN, CV, scanning electron microscope (SEM), transmission electon microscopy (TEM), electrochemical impendence spectroscopy (EIS), and charge-discharge tests. The results prove that the microspheres combine hollow structures inward and own a cubic spinel structure with space group of Fd-3m, high crystallinity, and excellent electrochemical performances. With the short Li⁺ diffusion length and hollow structure, the hierarchical LNMO microspheres exhibit 138.2 and 108.5 mAh g^?1 at 0.5 and 10 C, respectively. Excellent cycle stability is also demonstrated with more than 98.8 and 88.2 % capacity retention after 100 cycles at 1 and 10 C, respectively.     

A high-voltage lithium-ion battery prepared using a Sn-decorated reduced graphene oxide anode and a LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode

This paper describes the preparation and characterization of a high-voltage lithium-ion battery based on Sn-decorated reduced graphene oxide and LiNi_0.5Mn_1.5O₄ as the anode and cathode active materials, respectively. The Sn-decorated reduced graphene oxide is prepared using a microwave-assisted hydrothermal synthesis method followed by reduction at high temperature of a mixture of (C₆H₅)₂SnCl₂ and graphene oxide. The so-obtained anode material is characterized by thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and electron diffraction spectroscopy. The LiNi_0.5Mn_1.5O₄ is a commercially available product. The two materials are used to prepare composite electrodes, and their electrochemical properties are investigated by galvanostatic charge/discharge cycles at various current densities in lithium cells. The electrodes are then used to assemble a high-voltage lithium-ion cell, and the cell is tested to evaluate its performance as a function of discharge rate and cycle number.