LiNi0.5Mn1.5O4 Research Articles

Review—Multifunctional Separators: A Promising Approach for Improving the Durability and Performance of Li-Ion Batteries

Electrified vehicles require Li-ion batteries (LIBs) with 10-year useful life. We review herein our progress since 2016 in the understanding of dissolved Mn species and LIB performance degradation by multifunctional materials. Multifunctional separators (MFSs), can trap Mn cations, scavenge acid species, and/or dispense alkali metal ions, with significant battery performance benefits: increased capacity retention during electrochemical cycling and improved rate performance. Cells with LiMn2O4 (LMO), LiNi0.6Mn0.2Co0.2O2 (NCM622), or LiNi0.5Mn1.5O4 (LNMO) positive electrodes, graphite negative electrodes, and LiPF6/mixed organic carbonate solutions were investigated. XRD, ICP-OES, XANES, HR-SEM, FIB-SEM, and MAS-NMR on harvested cell components complemented and aided the interpretation of electrochemical test results. While in LIBs with positive electrodes affected by Mn dissolution cell performance improvements can be enabled by delaying and then impeding the deposition of transition metal (TM) ions deposition at negative electrodes through their trapping by MFS, acid scavenging separators provide a more general approach that can enable performance benefits in cells with non-spinel positive electrode materials such as NCM622, as well as with 5 V class positive electrode materials such as LNMO. We illustrate our discussion with both previously published and new data. We conclude with a discussion of remaining challenges, new opportunities, and recommendations for future work.

Effectively enhanced structural stability and electrochemical properties of LiNi0.5Mn1.5O4 cathode materials via poly-(3,4-ethylenedioxythiophene)-in situ coated for high voltage Li-ion batteries.

Spinel LiNi0.5Mn1.5O4 shows promise as a potential candidate for Li-ion batteries due to its high energy density and high rate performance. However, LiNi0.5Mn1.5O4 (LNMO) spinel oxides usually deliver poor cycle life because of the increasing impedance and gradually dissolving Mn resulting in the destruction of crystal structure. Here, a conductive polymer poly-(3,4-ethylenedioxythiophene) (PEDOT) surface modified strategy is introduced to settle the above challenges. The main purpose is to construct a uniform and dense shell film on the surface of LiNi0.5Mn1.5O4 (Industrial Grade), which is prepared by a simple chemical in situ oxidative polymerization method. The Mn dissolving from the lattice during the long-term cycling is well inhibited as the polymer shell protects LiNi0.5Mn1.5O4 from direct exposure to the highly active electrolyte. As expected, the 3 wt% poly-(3,4-ethylenedioxythiophene) coated sample reveals long cycle life with acceptable capacity of 114.5 mA h g−1 and high capacity retention of 91.6% after 200 cycles, compared to 70.9 mA h g−1 and 56.5%, respectively, for the bare LiNi0.5Mn1.5O4 sample. Furthermore, the coated sample demonstrates a higher capacity of 110 mA h g−1 and 63 mA h g−1 at 5C and 10C rate respectively. The improved performance is believed to be attributed to the formation of high conductivity and stable interface structure between electrolyte and LNMO, which is beneficial to suppress the destruction of crystalline structure due to the Mn dissolution and undesired side-reaction between electrolyte and LiNi0.5Mn1.5O4 in long cycle, and improve simultaneously the conductivity and interface stability of LiNi0.5Mn1.5O4 for high voltage lithium-ion batteries.

Identifying Contact Resistances in High-Voltage Cathodes by Impedance Spectroscopy

LiNi0.5Mn1.5O4 (LNMO) cathodes cycled versus a graphite anode at elevated temperatures usually show severe capacity fading upon extended charge/discharge cycling. In the literature, the impedance increase at the cathode is often related to the formation of a so-called cathode/electrolyte interphase (CEI) and is presented as one of the possible failure mechanisms. In this study, we show that the main reason for the increasing cathode impedance is a contact resistance (RCont.) between the aluminum current collector and the cathode electrode rather than a surface film resistance (RCEI). First evidence is presented by temperature-dependent impedance measurements and external compression of the electrode stack in the cell, which suggest an electronic nature of the commonly observed high-frequency semi-circle in a Nyquist plot. Further, by coating the LNMO cathode onto a glassy carbon disk, we demonstrate that the impedance increase arises from the interface between the cathode electrode and the aluminum current collector. Finally, we examine whether RCont. correlates with the release of protic species (e.g., HF) formed upon electrolyte oxidation. This is done by cycling graphite/LFP cells in the absence/presence of deliberately added HF, showing that a contact resistance upon cycling only develops upon HF addition.

Comparison of Electrochemical Degradation for Spray Dried and Pulse Gas Dried LiNi0.5Mn1.5O4

To commercialize next-generation cathode materials a lot of different synthesis methods need to be researched and evaluated regarding the attainable electrochemical properties of the materials on one hand, and the scalability of the process on the other. For the high voltage LiNi0.5Mn1.5O4 cathode material especially the degradation of the material during cycling needs to be investigated for different scales and techniques. LiNi0.5Mn1.5O4 (LNMO) was synthesized using two different methods in different scales: lab-scaled spray drying and pilot-scaled gas pulse drying. The materials were analysed by XRD, FESEM, particle size distribution and BET to achieve an extensive overview of the particles. The electrochemical properties were examined by galvanostatic charging and discharging at different C-rates as well as EIS at different SOCs using LiNi0.5Mn1.5O4/Li coins cells. To improve the electrochemical properties additional grinding and temperature treatments were used. Their influence on the electrochemical properties was investigated by analysing the capacity slippage as well as the electrolyte-, surface film- and the charge transfer resistance. These results will show that the same electrochemical properties can be achieved for the LiNi0.5Mn1.5O4 cathode material when changing and upscaling the synthesis methods.

Lithium bisoxalatodifluorophosphate (LiBODFP) as a multifunctional electrolyte additive for 5 V LiNi0.5Mn1.5O4-based lithium-ion batteries with enhanced electrochemical performance

Lithium bisoxalatodifluorophosphate (LiBODFP) is a promising multifunctional lithium salt-type electrolyte additive used to enhance the performance of 5 V LiNi0.5Mn1.5O4 (LNMO)-based lithium-ion batteries (LIBs).

Degradation of high-voltage cathodes for advanced lithium-ion batteries – differential capacity study on differently balanced cells

ABSTRACT The degradation of LiNi0.5Mn1.5O4 (LNMO) cathodes were investigated using different cell designs (half cells, full cells cathode-limited, anode-limited and cathode-limited with pre-charge). Half cells based on Li/LNMO show long-cycle stability due to the unlimited source of electrochemically available lithium. Full-cell configurations with Li4Ti5O12/LNMO are limited in their cycling performance and durability. Differential capacity studies during continuous cycling reveal a systematic intensity change of the NiII/III and NiIII/IV redox peaks as a function of the amount of electrochemically available lithium. As a mechanism, it could be clearly stated that the consumption of electrochemically available lithium determines the cycle stability. The decomposition of the active material itself (e.g. loss of Ni and Mn) is not crucial for the capacity loss. Thus, full cells with a pre-charged anode have the best cycling performance because of its high lithium content.

Improved rate performance of LiNi0.5Mn1.5O4 as cathode of lithium-ion battery by Li0.33La0.56TiO3 coating

Pristine LiNi0.5Mn1.5O4 (LNMO) and LNMO@LLTO (Li0.33La0.56TiO3) composites were synthesized by a sol-gel process. The lattice constant of LNMO increases with the increasing coated content of LLTO. All samples show irregular morphologies, and the particle size distributes uniformly between 200 and 500 nm. The inherent characteristic of Li0.33La0.56TiO3 with a large ionic conductivity decreases the interfacial charge transfer impedances, leading to an enhanced migration rate of Li-ions in the composite. As a cathode of LIBs, LNMO@LLTO (3 wt%) exhibits a large reversible capacity and a remarkable rate capability. Therefore, Li0.33La0.56TiO3 modification can be considered as an effective strategy to improve the rate capability of LNMO.

Structural and electrochemical characteristics of Al2O3-modified LiNi0.5Mn1.5O4 cathode materials for lithium-ion batteries

The high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) is a potential cathode material for lithium-ion batteries with outstanding energy density and power density. Here, we document a facile approach to prepare Al2O3-modified LNMO cathode materials. The Al2O3-modified LNMO materials were synthesized via a one-step solid-state reaction and then modified with Al2O3 via a wet chemical technique. The impacts of Al2O3 modification on the structure and electrochemical properties of LNMO materials were examined by X-ray diffraction, Fourier-transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, charge-discharge tests, cyclic voltammetry measurements, electrochemical impedance spectroscopy, and aging tests. Throughout the modification process, several Al3+ were noted to substitute for Ni2+, resulting in a decrease of Mn4+ to Mn3+; this increased the electronic conductivity and lowered the electrochemical polarization of the LNMO material. An amorphous Al2O3 coating layer developed on the surface of the LNMO particles in the modification, and this could alleviate the strike of HF caused by electrolyte decomposition as well as the development of a solid electrolyte interphase. Thus, the 0.5 wt% Al2O3-modified LNMO material had decreased Rsf and Rct and greater DLi values with a rate capability and cycling stability better than LNMO. The rate capability was 105.6 and 83.3 mAh g–1 at high C rates of 5 C and 7 C, as opposed to 83.3 and 54.9 mAh g–1, respectively; the room temperature (25 °C) capacity retention was 92.6% at 1 C after 200 cycles, as opposed to 87.0%. The high-temperature (55 °C) capacity retention was 90.9% at 1 C rate after 200 cycles as opposed to 86.5%. Thus, this is an easy and feasible method to improve the electrochemical performance of LNMO cathode materials for industrialization.

Enhancement of LiNi0.5Mn1.5O4 Cathode Materials through Interfacial Modification of Amorphous Al2O3 in Lithium Ion Batteries

Metal oxide modification can improve the electrochemical stability of cathodes and the cycle-life and rate capacity of rechargeable lithium ion batteries. Spinel LiNi0.5Mn1.5O4 (LNMO) has been considered as a promising cathode material for its high operating potential and high energy density. In this work, amorphous nano-Al2O3 with different thicknesses were applied to modify the surface of LNMO. Results of structure and surface analysis showed that the nano-Al2O3 film uniformly distributed on the surface of LNMO material without changing the crystal structure of the material. The electrochemical performances revealed that the capacity decay of bare LNMO materials focused on the first 50 cycles under room and elevated temperatures. It is essential to enhance the electrochemical performances of first 50 cycles. The capacity retention of the first 50 cycles was enhanced by the man made Al2O3 interface between active LNMO and electrolyte. The as-prepared surface modified LNMO material with the amount of Al2O3 at 1.77% exhibited superior rate and cycling performances under the room temperature even at elevated temperature. It also showed that the interfacial effect mechanism on the enhancement of LNMO performances is significantly important during the initial charging process (0%-20% SOC). In contrast to the impedance increasing with the SOC in the bare LNMO batteries, the resistance decreased dramatically in the first 20% SOC and almost kept constant during the following charging process. Both of the interface resistance between the cathode and electrolyte and charge transfer impedance were reduced, and the diffusion rate of lithium ion were improved.

Li4Ti5O12 epitaxial coating on LiNi0.5Mn1.5O4 surface for improving the electrochemical performance through solvothermal-assisted processing

During the charge-discharge of the LiNi0.5Mn1.5O4 (LNMO) cathode in Li-ion batteries, Ni2+ and Mn2+ dissolve in the electrolyte to cause oxidative decomposition, which is the major cause for fast capacity fading and poor cycle performance. Reducing the direct contact area between the cathode material and the electrolyte is a direct solution to improve the cell performance. This paper focuses on a solvothermal method to coat the surface of LiNi0.5Mn1.5O4 hollow microspheres with TiO2 followed by TiO2 conversion into Li4Ti5O12 (LTO) using LiOH·H2O. The Li4Ti5O12 coating layer synthesized by this method demonstrates epitaxial growth on the outer surface of LiNi0.5Mn1.5O4. The LTO-coated LNMO cathode exhibits capacity retention of 88.1% after 100 cycles at 0.5C rate, much higher than 62.2% for the bare LNMO counterpart, at elevated temperature of 55 °C. In addition, the Li+-ion mobility for the LTO-coated LNMO electrode is increased.

Hierarchical LiNi0.5Mn1.5O4 microspheres assembled with nanorice and their enhanced rates performance

Hierarchical LiNi0.5Mn1.5O4 (LNMO) microspheres were prepared via a hydrothermal method followed by program controlled temperature calcination. The as-obtained LNMO microspheres (diameter: ∼5 μm) which were assembled with submicron nanorices particles (length: ∼500 nm) (R-LNMO) could combine the superiority of the both nanosized and microsized structure, enhancing rates performance. The result indicated that R-LNMO exhibited discharge capacities of 141 mAh g−1 after 200 cycles at 2 C, together with the capacity retention of 95.2%. Besides, R-LNMO could deliver capacities of 147, 141, 137, 128, 120, 114 mAh g−1 at rates of 0.1, 2, 5, 10, 15 and 20 C, showing prospectively superior rates performance.

Effects of carbon coating on LiNi0.5Mn1.5O4 cathode material for lithium ion batteries using an atmospheric microwave plasma torch

A novel carbon coating method on LiNi0.5Mn1.5O4 (LNMO) cathode active material powders for lithium-ion batteries is reported. Carbon coated LNMO (LNMO/C) cathode is prepared by an atmospheric 2.45 GHz microwave plasma torch system using an acetylene gas as carbon precursor. This method is one-step process. Therefore, its method is not only an easy control, short manufacturing time, and low-cost operation, but also gives similar results on LNMO/C produced by other carbon coating methods. The morphology and structure of prepared samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) analysis, and elemental analyzer (EA). Electrochemical properties of LNMO/C are tested in lithium half coin cells. The results show that the carbon coating on LNMO could greatly enhance the rate capability and cycle performance especially at high temperature compared to bare LNMO. At 10 C rate with increased temperature, the discharge capacity is 0.15 mAhg−1 for bare LNMO, while 104 mAhg−1 for LNMO/C. Also, the capacity retention of LNMO/C sample is 97% at 0.5 C rate after 50 cycles at elevated temperature. The simple carbon coating method used in this work may easily provide a surface modification approach to other materials for commercialization.

Design of synergistic-coated layer of La2O3/Al2O3 in LiNi0.5Mn1.5O4 cathode for enhanced cycling stability and rate capability

LiNi0.5Mn1.5O4(LNMO) material has high theoretical capacity and high operating voltage. Nonetheless, LNMO has still many problems which include oxidative decomposition of electrolyte at high voltage and dissolution of transition metals into electrolyte. In this work, oxides of both La and Al (LAO) were coated on the surface LNMO by a wet chemical method. LAO is estimated to improve cycling performance (both room and elevated temperatures) and rate capability of LNMO due to the synergistic effect of La2O3 and Al2O3. Al2O3 can protect LNMO from the corrosion of HF that derives from decomposition of LiPF6, which results in mitigating the solution of Mn2+. Al2O3 can also prompt electrochemical reversibility of LNMO. La2O3 can enhance electrical conductivity, availing to charge transfer. Furthermore, La2O3 presents splendid thermal stability, which may boost the interfacial stability of LNMO. La2O3 can also alleviate the formation of the passive layer. The effect of coating content on performances of LNMO was also studied in detail. The capacity retention of 94.0% for the optimal coating LNMO with 4.0 wt.% (mLa2O3/mAl2O3 = 3: 1) is shown at 1 C and 25 °C after 200 cycles, and its capacity retention of 95.0% is exhibited at 1 C and 55 °C after 100 cycles. Its remarkable discharge capacities at 10, 15, and 20 C are 107.4, 94.4, and 82.7 mAh g−1, respectively, and its capacity retention of 93.3% is displayed at 5 C at room temperature after 500 cycles.

Stability analysis for 5V high energy density pouch batteries of Si anode and SL/EMC electrolytes

Currently, the effective way to improve energy density of lithium ion batteries may include choosing active materials that could guarantee both high voltage and high capacity. Herein, a pouch cell of 4.8 V was assembled by stacking several layers of (−) SiOC || LiNi0.5Mn1.5O4 (LNMO) (+) electrodes. Under wide voltage windows, the stability of the non-aqueous electrolyte is a great challenge. Ethylene carbonate (EC) are commonly used in LIBs, as the electrolyte can hardly withstand the high voltage above 4.5 V, but the sulfone (SL) solvent can keep stable under such condition. Even so, the structural stability of Si-based anode has to been considered in such batteries owing to the well-known volume expansion. The FEC additive was to improve the SEI formation for Si materials, and it was added into the SL-based electrolyte to study the compatibility of full cell for the first time. For pouch cell, the tri-electrode curves were measured during discharge process. And the volume changes and gas composition were recorded by a special equipment with respect to the charge voltage and cycling. Then, a failure mechanism and gas generation of the SiOC||LNMO system in both electrolytes was deduced, and the study of full (pouch) cells can guide the practical application.

Adaptation and improvement of an elemental mapping method for lithium ion battery electrodes and separators by means of laser ablation-inductively coupled plasma-mass spectrometry.

In this study, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was applied to previously aged carbonaceous anodes from lithium ion batteries (LIBs). The electrodes were treated by cyclic aging in a lithium ion cell set-up with LiNi0.5Mn1,5O4 (LNMO) cathodes and hard carbon (HC)/mesocarbon microbead (MCMB) anodes. An inhomogeneous transition metal deposition pattern could be induced by replacing the spacer in a standard coin cell set-up with a washer. The inhomogeneity pattern matched the dimension of the washer depicted by the hole in the center. These transition metal (TM) patterns were used to optimize higher lateral scanning speeds and frequencies on the spatial resolution of the mapping experiments using LA-ICP-MS. Higher scanning speeds had an observable influence on the resolution of the obtained image and an overall saving of 60% with regard to time and gas consumption could be achieved. Additionally, the optimized method was applied to the cathode and separator in order to visualize the distribution and deposition pattern, respectively.

Suppressed ionic contamination of LiNi0.5Mn1.5O4 with a Pt/ITO/stainless steel multilayer current collector

LiNi0.5Mn1.5O4 (LNMO) cathode thin films were prepared on Pt-coated stainless steel (SS) substrates by radio-frequency magnetron sputtering. The layers were post-annealed at 500, 600 and 700 °C to study the impact of thermal treatment on the crystallization of the cathode material. As the annealing temperature increases, interdiffusion occurs between the substrate and the LNMO film, which degrades the electrochemical properties of the cathode film. In order to mitigate this problem, an In-Sn-O (ITO) interlayer was introduced between Pt and the SS substrate. The ITO film is electrochemically stable and acts as an effective diffusion barrier between the substrate and the LNMO layer, which results in improved electrochemical properties of the LNMO film for a lithium ion battery.

Octahedral nano-particles constructed LiNi0.5Mn1.5O4 microspheres as high-voltage cathode materials for long-life lithium-ion batteries

The spinel LiNi0.5Mn1.5O4 (LNMO) cathode materials suffer from severe capacity fade during the charge-discharge process, which is caused by the instability of material structure under high voltage. Herein, a novel LNMO microsphere is prepared via simple co-precipitation method. The SEM images show that the LNMO spheres are constructed by many octahedral nano-particles. The structure stability of the LNMO cathode materials is improved so that the as-prepared LNMO cathode materials exhibit excellent electrochemical performance. It delivers a discharge capacity of 133.29 mA h g−1 at 0.2 C. Even the specific capacity still remains 127.46 mA h g−1 and the capacity retention rate is up to 95.6% after 300 cycles at 0.2 C. It is mainly attributed to the fact that the as-prepared LNMO materials expose the (111) crystal plane with the lowest surface energy.

Towards the Realization of Aqueous Electrode Processing for Sustainable High-Energy Lithium-Ion Cathodes

The rapidly growing use of lithium-ion batteries in a multitude of applications, ranging from handheld portable devices over electric bikes and scooters to (hybrid) electric cars and stationary energy storage, has awakened an increasing awareness for a more sustainable cell manufacturing. In fact, improving the environmental benignity of lithium-ion batteries is of utmost importance for their large-scale employment.1,2 To achieve this goal, all stages of cell fabrication must be taken into consideration. This includes not only the incorporation of non-toxic and readily available active materials, but also the development of environmentally-friendly and cheap binding agents, which can ideally be processed in water, thus sparing energy-intensive drying procedures and dry-room conditions and, as a result, turning the whole battery fabrication more eco-efficient. For graphite anodes, for instance, the utilization of water-soluble cellulose-based binders did not only render the use of toxic N-methyl-2-pyrrolidone as solvent unnecessary, but moreover led to substantial improvement in terms of cycling stability and first cycle coulombic efficiency.3,4 For the cathode side, however, the pronounced sensitivity of lithium transition metal oxides (e.g., LiNi0.5Mn1.5O4 (LNMO), Li[Ni1/3Mn1/3Co1/3]O2 (NMC), or Li2MnO3*NMC) towards water in combination with the resulting severe pitting corrosion of the aluminum current collector has so far prevented the implementation of aqueous binders and processing techniques.5–7 In this regard, our recent results, following a complementary approach to enable the aqueous processing of high-voltage LNMO by introducing suitable processing additives in order to stabilize the active material/water as well as the electrode/electrolyte/current collector interface, demonstrate the great potential to realize more sustainable lithium-ion cathodes. The synergistic interaction of an in situ surface coating of the active material particles paired with the crosslinking of the cellulose-based binder yields water-processed electrodes without pitting corrosion, enhanced cycling stability, improved rate performance, and overall higher specific capacities.8 Herein, we will address the remaining challenges encountered after establishing the aqueous lab-scale processing of these high-voltage lithium-ion cathodes to eventually achieve commercially viable cathode tapes, readily available for large-scale, high-energy lithium-ion batteries. These addressed challenges include improvements concerning the electrode to current collector adhesion, the binder distribution and electrode components cohesion, as well as the realization of highly stable cycling without a steady initial capacity increase and coulombic efficiencies, exceeding those for LNMO-based electrodes comprising the state-of-the-art poly(vinylidene difluoride) (PVdF) binder. References D. Larcher and J. M. Tarascon, Nat. Chem., 7, 19–29 (2015).C. J. Barnhart and S. M. Benson, Energy Environ. Sci., 6, 1083 (2013).H. Buqa, M. Holzapfel, F. Krumeich, C. Veit, and P. Novák, J. Power Sources, 161, 617–622 (2006).S. F. Lux, F. Schappacher, A. Balducci, S. Passerini, and M. Winter, J. Electrochem. Soc., 157, A320 (2010).X. Zhang et al., J. Power Sources, 196, 5102–5108 (2011).M. M. Thackeray, J. Am. Ceram. Soc., 82, 3347–3354 (1999).N. Loeffler et al., ChemSusChem, 9, 1112–1117 (2016).M. Kuenzel et al., ChemSusChem, 11, 562–573 (2018).

Engineering Surface Vacancy to Stabilize High-Voltage Battery Cathodes

In this issue of Chem, Cao and co-workers report a stabilization strategy for high-voltage lithium-ion battery cathodes down to the atomic scale. Using LiNi0.5Mn1.5O4 as a model, the authors demonstrated a protocol for precisely modulating the interstitial lattice sites on the material surface, showing the promising capability to improve electrochemical cyclability.

A novel boron-based ionic liquid electrolyte for high voltage lithium-ion batteries with outstanding cycling stability

Advanced ionic liquid-based electrolyte is herein characterized for the application in high voltage lithium-ion batteries. The electrolyte based on N-propyl-N-methylpiperidiniumdifluoro(oxalate)borate (PP13DFOB), lithium bis(trifluoromethanesulfonyl)-imide (LiTFSI) and dimethyl carbonate (DMC) is fully characterized in terms of anodic corrosion behavior, electrochemical properties and cathode-electrolyte interphase stability. Experimental and computational results show that the preferential oxidation of PP13DFOB results in a stable and low impedance solid electrolyte interface (SEI) film on the surface of LiNi0.5Mn1.5O4 (LNMO) cathode and a passivation layer on Al foil, which suppress transition metal dissolution and Al corrosion at high voltage. As a result, the Li/LNMO and Li/graphite coin cells with ionic liquid-based electrolyte achieve excellent electrochemical performance, displaying a discharge capacity of 121.2 mAh g−1 and 369.2 mAh g−1 after 100 cycles at 0.5 C respectively and demonstrating no distinct capacitance attenuation during charge-discharge cycles.