High-voltage Spinel LiNi0 Research Articles

Recent progress in the electrolytes for improving the cycling stability of LiNi0.5Mn1.5O4 high-voltage cathode

High-voltage spinel LiNi0.5Mn1.5O4 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, LiNi0.5Mn1.5O4-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 LiNi0.5Mn1.5O4-based batteries. Finally, an insight into the future research and further development of advanced electrolytes for LiNi0.5Mn1.5O4-based batteries is discussed.

Investigation on LiNi0.5Mn1.5O4 cathode material based on the precursor of nickel-manganese compound for lithium-ion battery

The high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) with submicron particle size (LNMO-8505P70010) has been synthesized based on nickel-manganese compound, which is obtained from pre-sintering the nickel-manganese hydroxide precipitation at 850 °C. The LNMO materials based on nickel-manganese hydroxide (LNMO-70010, LNMO-850570010, and LNMO-8501070010) have also been synthesized for comparison to study the pre-sintering impact on the properties of LiNi0.5Mn1.5O4 material. The morphologies and structures of the obtained samples have been analyzed by X-ray powder diffraction and scanning electron microscopy. The nickel-manganese compound has a spinel structure with high crystallinity, making it a good precursor to form high-performance LNMO with lower content of Mn3+ and impurity. The obtained LNMO-8505P70010 delivers discharge capacities of 125.4 mA h g−1 at 0.2 C, and the capacity retention of 15 C reaches 73.8 % of the capacity retention of 0.2​ C. Furthermore, it shows a superior cyclability with the capacity retention of 96.4 % after 150 cycles at 5 ​C. Compared with the synthesis method without pre-sintering, the synthesis method with pre-sintering can save energy while reaching the same discharge specific capacity.

Silicon Doping of High Voltage Spinel LiNi0.5Mn1.5O4 towards Superior Electrochemical Performance of Lithium Ion Batteries

Si doping at high voltage spinel LiNi0.5Mn1.5O4 are presented as an effective strategy to greatly increase the electrochemical performance. Well-crystallized LiNi0.5Mn1.5-xSixO4 (x=0.05, 0.10, 0.15, 0.20) with homogeneous Si distribution are successfully synthesized through solid-state reaction. Structural and electrochemical characteristics are investigated through FESEM, XRD, FTIR, Raman spectroscopy, cyclic voltammetry and galvanostatic charge/discharge testing. It can be demonstrated that Si doping significantly improves the electrochemical performance. LiNi0.5Mn1.35Si0.15O4 exhibits reversible capacities of 123 mAh/g after the 100th cycle at 0.5C and LiNi0.5Mn1.35Si0.15O4 as well as LiNi0.5Mn1.3Si0.2O4 show superior electrochemical stability over the pristine LiNi0.5Mn1.5O4 material. Since the Si-O bond exhibits high dissociation energy of 798kJ/mol (298K), which is far beyond of the dissociation energies of the Mn-O or Ni-O bonds, the excellent electrochemical performance might be associated with an increased structural and chemical stability caused by incorporation of Si into the Oxygen-rich crystal lattice.

Effects of Heat-Treatment on the Properties of Spinel LiNi0.5Mn1.5O4 Cathode Materials

High-voltage spinel LiNi0.5Mn1.5O4 (LNMO) were synthesized by a spray pyrolysis method followed by heat treatment at 900oC for 8 hours then post annealing at 700oC for varies duration (0-96 hours) under air atmosphere. The crystalline structure and morphology of the prepared samples are studied with X-ray diffraction (XRD), neutron powder diffraction (NPD), Raman spectroscopy, scanning electron microscope (SEM), and high-resolution transmission microscope (HR-TEM). The electrochemical properties of the prepared materials had also been investigated by the studies of cyclic voltammetry (CV) and the capacity retention with coin-type cells by use of battery testing system. The results show all of the prepared samples have similar morphology and average particle size, but crystalize into mixtures of ordered P4332 and disordered Fd-3 m phases with various fractions. It can be found from Table 1 that the phase fraction of ordered phase obtained from the Rietveld refinement of NPD patterns increases with increasing duration of post annealing at 700oC. Fig. 1 manifests the results of cycling performance of the coin cells comprised with the prepared samples at 0.1 and 1.0 C rates, respectively. Samples containing the higher phase fraction of disordered phase exhibits the lower capacity fade than those dominated with ordered phase. It may be attributed to the ordered phase dominated sample experienced more complex phase change than the disordered phase dominant sample, which had been revealed from the in-situ NPD studies. Figure 1

Systematic Tuning of the High Voltage Spinel LiNi0.5Mn1.5O4 By Modification of the Precursor and the Thermal Treatment

To further increase the effectiveness of lithium ion batteries an improvement especially in the energy density of the system is needed. High voltage cathode materials are a possible solution for solving this challenge. One potential high voltage material is LiNi0.5Mn1.5O4, which despite of its promising properties, has not been commercialized yet. A requirement for the commercialization of the cathode material is a systematic understanding of synthesis condition and their influence on the material properties. There are several synthesis routs described, which produce a precursor from acetates, nitrates, carbonates, sulfate or hydroxides, by solid-state, precipitation, sol-gel or spray trying for example and afterwards apply different temperatures and durations while the calcination of the precursor. All synthesis steps influence the properties of the material which leads into different electrochemical features for capacity, performance and cycle life. Therefore it is very hard the compare all the different synthesis routs and evaluate a systematic correlation. In my presentation I will show a chemical and procedural approaches, which not only will help to improve the electrochemical properties of LiNi0.5Mn1.5O4, but also can be scaled into an industrial dimension and focus on the variation of parameters which have not been discussed in full detail yet. There are several factors, which influence the electrochemical properties of LiNi0.5Mn1.5O4. Two of those are the amount of manganese(III) in the cathode material and a electrochemical inactive impurity phases. One important factor of influence for the formation of the manganese(III) content in LiNi0.5Mn1.5O4 and an impurity phase, which often consist of NixO and/or LixNi1-xO, is the oxygen content at the sample while the temperature treatment. [1] We used two different approaches to control the oxygen amount at the sample while the calcination. A chemical and a procedural approach where chosen. For the chemical method precursors with different composition of nitrate and acetate salts were used, which therefore changes the chemical composition of the precursor. Those salts show different gas removal at high temperature and therefore lead to a different environment for the sample while the calcination. For the procedural approach different kinds of calcination environments where used. By using a rotary kiln for example the resulting gas is removed similar for all the samples no matter the precursor used in comparison to a Muffle furnace. In our presentation we will present, that by changing the precursor chemistry the manganese(III) amount and the amount of impurity phase of the product can be tinkered. We will show, that the products exhibits a very different shape after the first calcination and therefore a different surface area. A different surface area means a different oxygen content at the sample. Resulting from this fact we will indicate the influence on the manganese(III) amount and the impurity phases. To achieve a systematic understanding all the synthesis materials were analyzed by electrochemical measurements, which will focus around capacity, cycle life and performance. The manganese amount will be calculated from the discharge curve, the impurity phase was analyzed by XRD measurements. Furthermore the samples were characterized by SEM, RAMAN to achieve information about the space group and BET to obtain information about the surface area of the samples. Furthermore we will show how to reduce the influence of those shapes by controlling the gas removal over using a rotary kiln. Resulting from this outcome the chemical and procedural approach can improve the electrochemical properties with rather easy ably able methods, which can be scaled into an industrial format. Acknowledgment The authors wish to thank for financial support by the BMBF (Bundesministerium für Bildung und Forschung) within the BaMoSa (Batterie – mobil in Sachsen) project. [1]Pasero, D. Reeves, N. Pralong, V. & West, A. R., J. Electrochem. Soc. 155, A282 (2008).

Effect of local structural changes on rate capability of LiNi0.5Mn1.5O4−δ cathode material for lithium ion batteries

High voltage spinel LiNi0.5Mn1.5O4 is a promising cathode material for the practical application in high energy density lithium ion batteries. With a simple strategy of cooling rate, the degree of ordering in disordered spinel LiNi0.5Mn1.5O4−δ structure is controlled at 0.5 °C min−1 for slow-cooled spinel and at 5 °C min−1 for fast-cooled spinel. From XRD and FTIR analyses and charge/discharge profiles, it is confirmed that the fast-cooled spinel develops more disordered structure than the slow-cooled spinel, retaining more oxygen vacancies and more abundant Mn3+. By using in situ XRD analysis, the more disordered spinel follows the extended solid-solution reaction in favor of Li+ transport, which results in an improved rate capability. Moreover, through ex situ XAS analysis and the more quantitative results from EXAFS fitting, the local structural changes in the vicinity of Mn and Ni cations are investigated at various C-rates and smaller structural distortion in more disordered spinel is proposed to enhance the rate capability.

The effect of cobalt doping on the morphology and electrochemical performance of high-voltage spinel LiNi0.5Mn1.5O4 cathode material

To reveal the effects of Co-doping on the electrochemical performance of micro-sized LiNi0.5Mn1.5O4 (LNMO), undoped LNMO and Co-doped LiCo0.1Ni0.45Mn1.45O4 (LCoNMO) are synthesized via a PVP-combustion method and calcined at 1000°C for 6h. SEM and XRD analyses suggest that Co-doping decreases the particle size and the LizNi1-zO2 impurity at the calcination temperature of 1000°C. LCoNMO has much better rate capability while its specific capacity at C/5 is 10% lower than that of LNMO. At 15C rate, their specific capacities are closed, and the LCoNMO delivers 86.2% capacity relative to C/5, and this value for LNMO is only 77.0%. The DLi+values determined by potential intermittent titration technique (PITT) test of LCoNMO are 1–2 times higher than that of LNMO in most SOC region. The LCoNMO shows very excellent cycling performance, which is the best value compared with literatures. After 1000cycles, the LCoNMO still delivers 94.1% capacity. Moreover, its coulombic efficiency and energy efficiency keep at 99.84% and over 97.3% during 1C cycling, respectively.

Studies of a layered-spinel Li[Ni1/3Mn2/3]O2 cathode material for Li-ion batteries synthesized by a hydrothermal precipitation

This work continues our research on integrated “layered-spinel” high-capacity cathode material Li[Ni1/3Mn2/3]O2 [30]. This material operated at potentials >4.6V and demonstrated an advantageous cycling stability compared to high-voltage spinel LiNi0.5Mn1.5O4. In the present study, the Li[Ni1/3Mn2/3]O2 material was synthesized by a hydrothermal precipitation. The Rietveld analysis of XRD patterns indicated the presence of two layered structure phases: a monoclinic Li2MnO3 (about 58%) and a rhombohedral LiNiO2 (24%), along with spinel LiNi0.5Mn1.5O4 (17%) and rock salt Li0.2Mn0.2Ni0.5O (1%) phases. We demonstrate an interesting phenomenon of this electrode activation upon cycling from 100 to 220 mAh g−1 in the potential range of 2.3–4.9V and stabilization followed by lowering the capacity to 89.5% of the maximal value after 100 cycles. It is suggested that the high capacity resulted from the activation of Li[Li1/3Mn2/3]O2 and participation of spinel component upon cycling to potential ≥4.5V.

Development of a benchmarking model for lithium battery electrodes

This paper presents a benchmarking model to enable systematic selection of anode and cathode materials for lithium batteries in stationary applications, hybrid and battery electric vehicles. The model incorporates parameters for energy density, power density, safety, lifetime, costs and raw materials. Combinations of carbon anodes, Li4Ti5O12 or TiO2 with LiFePO4 cathodes comprise interesting combinations for application in hybrid power trains. Higher cost and raw material prioritization of stationary applications hinders the breakthrough of Li4Ti5O12, while a combination of TiO2 and LiFePO4 is suggested. The favored combinations resemble state-of-the-art materials, whereas novel cell chemistries must be optimized for cells in battery electric vehicles. In contrast to actual research efforts, sulfur as a cathode material is excluded due to its low volumetric energy density and its known lifetime and safety issues. Lithium as anode materials is discarded due to safety issues linked to electrode melting and dendrite formation. A high capacity composite Li2MnO3·LiNi0.5Co0.5O2 and high voltage spinel LiNi0.5Mn1.5O4 cathode with silicon as anode material promise high energy densities with sufficient lifetime and safety properties if electrochemical and thermal stabilization of the electrolyte/electrode interfaces and bulk materials is achieved. The model allows a systematic top-down orientation of research on lithium batteries.

Origin of the Ni/Mn ordering in high-voltage spinel LiNi0.5Mn1.5O4: The role of oxygen vacancies and cation doping

Spinel LiNi0.5Mn1.5O4 (LNMO) exhibits two different Ni/Mn arrangements, i.e., the Ni/Mn ordered P4332 phase and disordered Fd-3m phase. It has been found that the Ni/Mn disorder is correlated with the formation of oxygen vacancies, nevertheless the underlying mechanism remains unclear. Density functional theory (DFT) calculations show that formation of 1:3 ordered Ni2+ and Mn4+ ions is energetically favorable compared to the disordered Ni3+ and Mn3+ ions caused by Ni aggregation in the stoichiometric P4332 phase. However, in oxygen deficient LiNi0.5Mn1.5O4−δ, the oxygen vacancies tend to diminish the valence discrepancy between the Ni aggregated and the ordered P4332 phases, making the former energetically competitive and consequently resulting in the disordered Ni/Mn distribution. Understanding the origin of Ni/Mn disorder also sheds light on the cation doping effect. Calculations show that Mg2+ ion tends to replace Ni2+ ion in ordered P4332 phase, and maintaining the Ni/Mn order. By contrast, Al doping promotes the Ni/Mn disorder, as Al3+ ion prefers to substitute for Ni3+ and Mn3+ ions emerged in Ni/Mn disordered structure. Our findings rationalize the experimental observations, and further reveal that Ni/Mn arrangement could be controlled by adjusting the electronic structure of spinel LNMO system.

Facile synthesis of well-shaped spinel LiNi0.5Mn1.5O4nanoparticles as cathode materials for lithium ion batteries

High voltage spinel LiNi0.5Mn1.5O4nanoparticles with polyhedral shapes were synthesized by a solid state reaction using α-MnO2nanowires as precursors.

Exploiting chemically and electrochemically reactive phosphite derivatives for high-voltage spinel LiNi0.5Mn1.5O4 cathodes

A family of organophosphorus compounds including triphenyl phosphite (TPP), trimethyl phosphite (TMP), tris(2,2,2-trifluoroethyl) phosphite (TFEP), and tris(trimethylsilyl) phosphite (TMSP) is investigated as additives for the stabilization of high-voltage LiNi0.5Mn1.5O4 (LNMO) cathode-electrolyte interface. Our investigation reveals that the cycling performance of Li/LNMO half cells with the TMP, TFEP or TMSP additive is drastically improved at 60 °C compared to the baseline electrolyte. Among the various phosphite-based additives tested, TMSP additive enables facile Li ion transport at high C rates and significantly enhances the storage performance of the Li/LNMO cells at 60 °C. To understand the effects of the phosphite-based additives on electrolyte oxidative decomposition at high voltages, the surface chemistry of the cathode after precycling is investigated via ex-situ X-ray photoelectron spectroscopy (XPS). Additionally, the roles of phosphite-based additives to suppress LiPF6 hydrolysis and to remove HF are examined via 19F and 31P NMR spectroscopies.

Influence of surface modification on electrochemical performance of high voltage spinel ordered-LiNi0.5Mn1.5O4 exposed to 5.3 V for 100 h before and after surface modification with ALD method

To quantify the effect of high voltage on the electrochemical properties of high-potential spinel ordered-LiNi0.5Mn1.5O4, it was intentionally exposed to 5.3V for 100h that can ensure the decomposition of electrolyte. After this treatment, the bulk structure did not change, but electrochemical properties of the sample were severely degraded; polarization became large and capacity loss was substantial. Polarization was caused by formation of a thick insulating passivation layer on the surface of the sample that was measured by impedance spectroscopy. The capacity loss can be partially caused by incomplete phase transformation during discharging as a result of loss of electrical contact due to the presence of the thick passivation layer on the surface of particles. This indicates that the phase transformation depends on the applied current. The other cause for the capacity loss can be from the inactiveness of transition metals in the surface that was measured by XPS. Thick passivation layer on the surface can have inactive transition metals leading to permanent capacity fading. Hence, to control the electrode stability in high voltage spinel LiNi0.5Mn1.5O4, a bare LNMO sample coated with Al2O3 by Atomic Layer Deposition (ALD) were prepared, then exposed to 5.3V for 100h. After this surface treatment, the Al2O3-coated sample showed much better electrochemical performance than the bare sample. During the exposure, the bare sample underwent intensive surface reactions with very large generated current density and large charge-transfer resistance. In contrast, the coated sample experienced much weaker surface reactions with low charge-transfer resistance even though the applied potential, 5.3V was much higher than the stable upper voltage limit (∼4.5V) of conventional electrolyte. The coating effectively protects the surface of the material from surface reactions such as oxidation of the electrolyte; therefore Al2O3-coated LNMO shows reasonable electrochemical properties after exposing at 5.3V for 100h. This finding demonstrates that detrimental effects of the exposure at high potential on the electrochemical properties strongly depends on surface characteristics. This understanding can be used to stabilize high-voltage positive electrode materials.

Truncated octahedral LiNi0.5Mn1.5O4 cathode material for ultralong-life lithium-ion battery: Positive (100) surfaces in high-voltage spinel system

So far, it has not yet reached an agreement that (111) surfaces or (100) surfaces are more positive to electrochemical performance in the spinel system. Herein, we present the synthesis of regular truncated octahedral high-voltage spinel LiNi0.5Mn1.5O4 single crystals with preferred growth of (100) surfaces, which incredibly exhibit the best long-term cycling stability compared with the state-of-art spinel material. The capacity retention is about 90% after 2000 cycles at 1 C. The extraordinary performance is mostly attributed to the highly regular truncated octahedral microstructure with large portions of stable (100) facets, which can stabilize the spinel structure to effectively suppress the side reactions with the electrolyte at high operating voltage and are also orientated to support Li+ transport kinetics. Therefore, our work further promotes the practical application of LiNi0.5Mn1.5O4 cathode material in next generation Lithium-ion batteries with high energy density and power performance.

Investigation on preparation and performance of spinel LiNi0.5Mn1.5O4 with different microstructures for lithium-ion batteries.

The high voltage spinel LiNi0.5Mn1.5O4 is a promising cathode material in next generation of lithium ion batteries. In this study, LiNi0.5Mn1.5O4 with various particle microstructures are prepared by controlling the microstructures of precursors. LiNi0.5Mn1.5O4 spinel samples with solid, hollow and hierarchical microstructures are prepared with solid MnCO3, hollow MnO2 and hierarchical Mn2O3 as precursor, respectively. The homemade spinel materials are investigated and the results show that the content of Mn3+ and impurity phase differ much in these three spinel samples obtained under the same calcining and annealing conditions. It is revealed for the first time that an inhomogeneous migration of atoms may introduce Mn3+ and impurity phase in the spinel. The hierarchical microstructure with the primary particles interconnected is optimal for electrode materials because this microstructure has a higher conductivity between the interconnected primary particles and appropriate specific surface area. LiNi0.5Mn1.5O4 in this microstructure has the best rate capability and also the best long-term cycling stability.

High electrochemical performance of high-voltage LiNi0.5Mn1.5O4 by decoupling the Ni/Mn disordering from the presence of Mn3+ ions

Electrochemical activity in high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) is strongly affected by the disordering of Ni/Mn and the presence of Mn3+ ions. However, understanding the effect of the Ni/Mn disordering or the presence of Mn3+ ions on electrochemical properties is not trivial because disordering is typically coupled with the presence of Mn3+ ions. Here, we demonstrate for the first time that the doping of Li instead of Ni increases Ni/Mn disordering, which is decoupled from the presence of Mn3+ ions. The resultant material has a particle size of ~1–2 μm and can achieve 120 mAh g−1 at 10 C for 50 cycles and further deliver about 60 mAh g−1 even at a rate of ~60 C (1 min discharge). Superior electrochemical performance is achieved by increased solid-solution phase transition behavior, which is caused by increased Ni/Mn disordering during delithiation. By decoupling, we find that the electrochemical properties in LNMO strongly depend on the phase transformation behavior and that the Ni/Mn disordering, rather than Mn3+ ions, affects the phase transformation by increasing the solid-solution reaction. The fundamental understanding gained from this work could be applied to the development of other phase-separating compounds to improve their electrochemical performance. Doping LiNi0.5Mn1.5O4 (LNMO) with Li instead of Ni significantly improves its electrochemical performance, find scientists in Korea. Cathode materials with high redox potentials are needed to realize lithium-ion batteries with high energy densities. The high-voltage spinel LNMO is a promising cathode material, but its electrochemical performance is strongly affected by the disordering of Ni/Mn in the presence of Mn3+ ions. Now, Junghwa Lee, Chaeah Kim and Byoungwoo Kang at Pohang University of Science and Technology in Korea have found that doping LNMO with Li decouples Ni/Mn disordering from the presence of Mn3+ ions. This significantly improves its electrochemical performance through enhanced solid-solution phase transition. The researchers anticipate that the results of the current study can be used to improve the electrochemical performance of other phase-separating compounds. We at the first time demonstrate that the Ni/Mn disordering in LNMO spinel is decoupled from the presence of Mn3+ ions by doping Li and strongly affects phase transformation resulting in the increase of solid-solution phase transformation. The resulting material with 1–2 μm achieves superior rate capability, 120 mAh g−1 at ~38 C and 60 mAh g−1 at 60 C.

Synthesis of high-voltage spinel LiNi0.5Mn1.5O4 material for lithium-ion batteries by a metal-cholate supramolecular hydrogel as precursor

High-voltage cathode material LiNi0.5Mn1.5O4 has been first synthesized by a novel metal-cholated supramolecular hydrogel as precursor. The structural analysis was investigated by X-ray powder diffraction, scanning electronic microscope, and Fourier transform infrared spectroscopy. The results indicated that the as-products possessed well constructed spinel structure and high crystallinity and pure phase through adding optimal amount of cholic acid. The electrochemical properties were also investigated, and its results showed that the LiNi0.5Mn1.5O4 material exhibited enhanced rate capacity and cycling properties as electrode materials in lithium cells mainly due to the improved crystallinity and higher pure phase. In a word, this new approach provides an alternative and promising route for the fabrication of cathode materials with perfect octahedron structure and excellent electrochemical properties using metal-driven hydrogels as template.

The Effect on Electrochemical Properties By the Content of Mn3+ of High-Voltage Spinel LiNi0.5Mn1.5O4 Cathode Material for Highly Stable Lithium-Ion Batteries

High voltage spinel LiNi0.5Mn1.5O4 (LNMO) is considered as one of the most promising cathode material for next generation lithium ion batteries, which can greatly meet the rapid increasing demand of power sources applied into portable electronic devices and electric vehicles. The electrochemical performance of LNMO is greatly affected by the morphology and lattice structure. In order to improve the long-term cycling stability, particularly at elevated temperature, one of effective methods is to tune the amount of Mn3+ in LNMO for controlling the stability of spinel lattice structure due to complex interactions on the interface of electrode material and the electrolyte on the high operating voltage. In this work, the influence of different content of Mn3+ in LNMO on electrochemical properties is displayed by truncated octahedral LNMO obtained by controlling synthetic conditions of heating atmosphere and temperature cooling rate. Superior truncated octahedral LNMO materials were synthesized with tuned Mn3+ content through heating under oxygen atmosphere and controlling the cooling conditions of natural cooling and a cooling rate of 5 oC/min, respectively. The material synthesized under O2 shows the smallest amout of Mn3+, while the one with natural cooling has the highest amount. The LNMO material obtained under O2 shows the best electrochemical stability with about 96% capacity retention after 500 cycles at 0.5C (1C = 147 mA/g). The material obtained at 5 oC/min shows about 90% of capacity retention after 2000 C cycles at 1C, while the one obtained with natural cooling can reach up to 88% of capacity retention after 500 cycles at 0.5C at 60 oC. Therefore, the Ni-Mn disordering intrinsically related to the Mn3+ amount has a great effect on the electrochemical performance of LNMO. More experimental details and measurement results will be exhibited later. Reference: 1. Xiao, J., Chen, X., Sushko, P., et al, Adv. Mater. 2012, 24, 2109. 2. Chemelewski, K. R.; Lee, E.; Li, W.; Manthiram, A. Chem. Mater. 2013, 25, 2890.

Improved Electrochemical Performance of Multi-Phase Layered-Spinel Cathodes for Li-Ion Batteries

Li-ion batteries are implemented as the major power source for portable electronic devices because of their high energy density and long cycle-life. High capacity cathode materials are essential to increase the energy density of Li-ion batteries within the stability of standard electrolyte solutions. Layered LiNi1/3Mn1/3Co1/3O2 and high voltage spinel LiNi0.5Mn1.5O4 are promising cathode materials as these can provide specific capacities of 160 and 130 mAh g-1, respectively. It is known that LiNi1/3Mn1/3Co1/3O2 exhibits good cycling stability when cycled in the potential range of 2.5-4.3 V vs. Li/Li+ [1-3] and undergoes severe capacity fading upon cycling to potentials ≥ 4.5 V [4, 5]. Similarly, spinel LiNi0.5Mn1.5O4 is usually cycled in the potential range of 3.5-4.9 V [6, 7]. When cycled to potential lower than 3.5 V in order to increase the specific capacity, it also undergoes capacity fading upon cycling, due to structural instability arising from a well-known Jahn-Teller effect [8, 9]. Recently, Li and Mn-rich layered compounds with a general composition xLi2MnO3.(1-x)LiMO2 (M=Mn, Co and Ni) are considered as attractive cathode materials for high energy Li-ion batteries as these materials can provide capacities ≥ 250 mAh g-1. Li-rich layered-spinel composites are also explored as high capacity cathodes which can exhibit capacities ≥ 200 mAh g-1 within a wide potential range of 2.0-5.0 V [10-12]. Thus, multiphase cathodes may be found advantageous as compared to single phase, i.e., either layered or spinel cathode materials. In the present study, we have synthesized layered-spinel composite cathode materials LiNi1/3Mn2/3O2 and LiNi0.33Mn0.54Co0.13O2 involving Li2MnO3 (monoclinic), LiNiO2 (rhombohedral) and LiNi0.5Mn1.5O4 (spinel) by self-combustion reaction (SCR). The Reitveld analysis and TEM study clearly indicates the presence of these phases. Interestingly, these cathode materials exhibited superior cycling stability when cycled in a wide potential range of 2.3-4.9 V vs. Li (Fig. 1). LiNi1/3Mn2/3O2 exhibited an initial specific capacity of 80 mAh g-1 which increased to about 220 mAh g-1 after 20 cycles and then a stable capacity is observed even after 100 cycles. On the other hand, the specific capacity decreases from 190 to 150 mAh g-1 with 79 % capacity retention for the spinel LiNi0.5Mn1.5O4. Also, LiNi0.33Mn0.54Co0.13O2 exhibited a stable specific capacity of about 170 mAh g-1 after 100 cycles when cycled in the potential range of 2.3-4.9 V. On the other hand, the specific capacity of LiNi0.33Mn0.33Co0.33O2 decreased from 208 mAh g-1 to a value of 130 mAh g-1 after only 50 cycles. The structural studies of cycled electrodes indicate that the spinel content in the active mass increases upon cycling due to structural layered-to-spinel transformation. However, the presence of untransformed Li2MnO3 in the active mass stabilizes the structure even after cycling in a wide potential range. These results indicate that neither layered nor spinel can be cycled in a too wide potential range while multiphase layered-spinel cathode materials can be cycled in a wide potential range with a stable high specific capacity in Li-ion batteries. Thus, the order of stability of these cathode materials can be presented as layered-spinel> spinel > layered. References T. Ohzuku, Y. Makimura, Chem. Lett., 7, 642 (2001).H. Sclar, D. Kovacheva, E. Zhecheva, R. Stoyanova, R. Lavi, G. Kimmel, J. Grinblat, O. Girshevitz, F. Amalraj, O. Haik, E. Zinigrad, B. markovsky, D. Aurbach, J. Electrochem. Soc., 156, A938 (2009).S.K. Martha, H. Sclar, Z.S. Framowitz, D. Kovacheva, N. Saliyski, Y. Gofer, P. Sharon, E. Golik, B. Markovsky, D. Aurbach, J. Power Sources, 189, 248 (2009).X. Li, Y.J. Wei, H. Ehrenberg, F. Du, C.Z. Wang, G. Chen, Solid State Ionics, 178, 1969 (2008).P.K. Nayak, J. Grinblat, M. Levi, Y. Wu, B. Powell, D. Aurbach, J. Electroanal. Chem., 733, 6 (2014).Y. Xue, Z. Wang, F. Yu, Y. Zhang, G. Yin, J. Mater. Chem. A, 2, 4185 (2014).Y. Talyosef, B. Markovsky, G. Salitra, D. Aurbach, H.-J. Kim, S. Choi, J. Power Sources, 146, 664 (2005).M. Okubo, Y. Mizuno, H. Yamada, J. Kim, E. Hosono, H. Zhou, T. Kudo, I. Honma, ACS Nano, 4, 741 (2010).C.Y. Ouyang, S.Q. Shi, M.S. Lei, J. Alloys Compd., 474, 370 (2009).E.-S. Lee, A. Hug, H.-U. Chang, A. Manthiram, Chem. Mater., 24, 600 (2012). S.-H. Park, S.-H. Kang, C.S. Johnson, K. Amine, M.M. Thackeray, Electrochem. Commun., 9, 262 (2007).D. Luo, G. Li, C. Fu, J. Zheng, J. Fan, Q. Li, L. Li, Adv. Energy Mater., 4, 1400062 (2014). Figure 1

Implementation of Stable Surface Structures; A Promising Key to Solve Capacity Fading Issues for the High-Voltage LiNi0.5Mn1.5O4

High-voltage spinel LiNi0.5Mn1.5O4 (LNMO) cathode materials allow three-dimensional lithium-ion diffusion in its lattice, which makes it unique among various high-voltage cathode materials. The structural changes and Mn ion dissolution of the LNMO cathode materials are some of the critical properties affecting its performance degradation, although it is considered to be a promising high-energy and high-power density cathode material for Li-ion batteries.1-3 In this study, our group extensively investigated the structural changes at the surface and bulk, where we adopted polyol process (Fig. 1) as a new method of synthesizing LNMO materials. New findings on the structural stability related to the transition metal (TM) migration are discovered for LNMO synthesized via conventional sol-gel method (SG-) versus polyol process (P-). Fig. 2a presents the relation between specific capacity and cycle number of SG- and P-LNMO. Initially, SG-LNMO has larger capacity, but the capacity of SG-LNMO degrades drastically (>50% loss of its initial capacity) even in 100cycles under high temperature 55 oC. In-depth local structural variations at the surface and bulk around Mn during cycled-aging were studied via in situ extended X-ray absorption fine structure (EXAFS) spectra. The Fourier-transformed (FT) EXAFS spectra from both transmission electron yield (TEY) and fluorescence yield (FY) mode (k3-weighted in k-space, but not phase-corrected FT, causing shorter bond lengths in the plots than for the actual bonds) at Mn K-edge are studied. For the Mn K-edge results shown in FY mode, there were negligible alterations in both the Mn-O and Mn-TM bond length from the pristine to 20th cycled state, indicating that Mn in both materials is stable and maintains its original structure within the bulk site. On the other hand, the spectral changes during cycled-aging in TEY mode, the shift of the Mn-TM bond length and the emergence of the Mn-TMtet can be observed only on the SG-LNMO. It means the migration of Mn cations (mostly Mn2+) to the surface, which is well-known phase transition phenomenon in LNMO cathode materials. Surprisingly, P-LNMO does show structural and phase stability by looking at the spectra on both at the bulk and surface even after 20th cycled. The local atomic-level crystal structures were further investigated via aberration-corrected scanning transmission electron microscopy (STEM) taken along the [110] crystallographic direction. Surface regions (~1 nm) of the cycle-aged SG-LNMO particles showed two types of local atomic-level transition metal (TM) ions migration, which is closely related to Mn ion dissolution. TM ions replace tetrahedral Li sites to form a Mn3O4-like structure, and fill the empty octahedral sites to form a rocksalt-like structure, whereas the cycle-aged P-LNMO maintained its original spinel structure. It points to a pathway toward the promising solution to prevent capacity degradation with increased structural stability against Mn dissolution. We correlated such capacity fading issues to local structural changes and more detailed results of them will be presented at the meeting. Acknowledgements H. Yoon and H. Cho acknowledge S. Khalid for technical assistance at the National Synchrotron Light Source for the use of beamline X18B. The double aberration-corrected scanning TEM (TEAM0.5) was performed with an approval of the National Center for Electron Microscopy at the Lawrence Berkeley National Laboratory (Proposal No. 3162). Reference 1. J. Song, D. W. Shin, Y. Lu, C. D. Amos, A. Manthiram and J. B. Goodenough, Chem. Mat., 2012, 24, 3101-3109. 2. N. M. Hagh, F. Cosandey, S. Rangan, R. Bartynski and G. G. Amatucci, J. Electrochem. Soc., 2010, 157, A305-A319. 3. D. Liu, W. Zhu, J. Trottier, C. Gagnon, F. Barray, A. Guerfi, A. Mauger, H. Groult, C. M. Julien, J. B. Goodenough and K. Zaghib, RSC Advances, 2014, 4, 154-167. Figure 1