Spinel LiNi0 Research Articles

The CeF4-coated spinel LiNi0.5Mn1.5O4 with improved electrochemical performance for 5 V lithium-ion batteries

The CeF4-coated spinel LiNi0.5Mn1.5O4 with improved electrochemical performance for 5 V lithium-ion batteries

Spinel LiNi0.5Mn1.5O4 shell enables Ni-rich layered oxide cathode with improved cycling stability and rate capability for high-energy lithium-ion batteries

Increasing the charging cut-off voltage is an effective strategy to achieve high energy density Ni-rich layered oxide cathode materials, however the dramatic deterioration of cycling lifespan and thermal stability still remain great challenges in large-scale practical applications. Herein, a rationally designed core-shell structure LiNi0.9Co0.1O2@LiNi0.5Mn1.5O4 composite composed of spinel structure Mn-rich LiNi0.5Mn1.5O4 shell and layered structure Ni-rich LiNi0.9Co0.1O2 core is proposed to enhance the structure stability and thermal stability under high-voltage application scenario. Compared to the pristine LiNi0.9Co0.1O2 cathode, the core-shell structure LiNi0.9Co0.1O2@LiNi0.5Mn1.5O4 composite with optimized LiNi0.5Mn1.5O4 shell exhibits high reversible specific capacity (195.5 mA h g − 1 at 0.5 C), remarkable cycling stability (86% capacity retention after 100 cycles) and superior rate capability (162.5 mA h g − 1 at 5.0 C) within 2.8 V-4.5 V. The comprehensively improved electrochemical performance is mainly attributed to the Mn-rich LiNi0.5Mn1.5O4 shell, which not only effectively prevents the phase transition and microstructural collapse, but also ameliorates the Li+ transport ability, high-voltage charging capability and thermal stability. Such novel core-shell structure LiNi0.9Co0.1O2@LiNi0.5Mn1.5O4 composite as promising cathode is highly expected to greatly promote the practical application of high energy density lithium-ion batteries.

High-voltage lithium-ion capacitors enabled by a multifunctional phosphite electrolyte additive

Combining the high energy of lithium-ion batteries with the high power and excellent cycling stability of supercapacitors, lithium-ion capacitors (LICs) stand for an emerging hybrid technology for next-generation electrochemical energy storage. Among them, the configuration composed of a battery-type cathode and a capacitor-type anode is advantageous owing to its unnecessity for electrode prelithiation but disadvantageous because of its limited operating voltage. Herein, using triphenyl phosphite (TPPi) as a powerful multifunctional electrolyte additive to not only scavenge electrolyte impurities but also form robust, uniform, and thin cathode/electrolyte interface film on cathode and solid-electrolyte interphase film on anode, we develop high-voltage LICs from a high-potential spinel LiNi0.5Mn1.5O4 cathode and an activated carbon anode. In addition to the important multifunctionalities of TPPi, we modulate the capacity ratio between the cathode and anode and composite the electrodes with carbon nanotubes (CNTs) to enhance the overall performance for our LICs. Therefore, having the synergy from the multifunctionalities of TPPi, capacity modulation between the cathode and anode, and electrode compositing with CNTs, the optimized LIC shows a high operating voltage of 3.45 V, high energy density of 61.6 Wh kg−1, high power density of 52.5 kW kg−1, and long cycle life with a capacity retention of 91.8% after 6000 cycles, outperforming all of its previously reported counterparts having a similar configuration incorporating a battery cathode and a capacitor anode. The rational strategy developed in this work is versatile and should be applicable to other electrode/electrolyte systems for advanced hybrid electrochemical energy storage.

Growth Parameters and Diffusion Barriers for Functional High-Voltage Thin-Film Batteries Based on Spinel LiNi0.5Mn1.5O4 Cathodes.

Cobalt-free spinel LiNi0.5Mn1.5O4 is one of the most promising and environmentally friendly cathodes, based on its high specific theoretical capacity (147 mAh·g-1) and high electrochemical potential (4.7 V vs Li+/Li), as well as good electronic and Li-ion conductivities. In this work, we present the fabrication of LiNi0.5Mn1.5O4 thin-film cathodes deposited by the industrially scalable AC magnetron sputtering technique on functional and cost-effective stainless steel current collectors. This is the first step toward battery downscaling, envisioning the fabrication of compact microbatteries for low-power energy supply. The thin-film strategy is crucial also for solid electrolyte fabrication that will allow the integration of high-energy-density batteries while overcoming most of the current battery challenges. In this work, the effect of film thickness on the material's electrochemical performance is discussed, correlating the observed structural and morphological evolution with the final electrochemical response. Moreover, the effect of iron diffusion from the current collector substrate into the cathode film is analyzed. The addition of a stable CrN barrier layer in between the substrate and the film is proposed to prevent Fe diffusion, with a direct positive influence on the electrochemical behavior. All in all, the obtained results will facilitate the practical implementation of LiNi0.5Mn1.5O4 thin films as high-voltage cathodes in functional cost-effective microbatteries.

Role of Carbon Nanotube in Preparation of Spinel Lini0.5mn1.5o4 Cathode

Role of Carbon Nanotube in Preparation of Spinel Lini0.5mn1.5o4 Cathode

Achieving superior high-rate cyclability of LiNi0.5Mn1.5O4 cathode material via constructing stable CuO modification interface

The spinel LiNi0.5Mn1.5O4 (LNMO) is an attractive high-voltage cathode material for commercial lithium-ion batteries because of its high energy density and low cost. However, surface side reactions and Mn dissolution during the cycling process damage the electrochemical performances of the material, especially at high rates. In this paper, the CuO coating is successfully constructed to stabilize the surface structure of LNMO. The CuO layer increases the degree of disorder phase and acts as a stable shell to inhibit the dissolution of Mn. The CuO-coated samples present the excellent rate performance and cyclability. Even at 10C rate, the CuO-coated LNMO (Cu 0.8 wt%) exhibits a high initial capacity of 128.7 mAh g−1 with a capacity retention rate of 95.3% after 100 cycles at 3.5–4.8 V. A series of test results demonstrate that the excellent performance is attributed to the CuO coating enhancing the structural stability of the material and improving the diffusion rate of lithium ion.

From coating to doping: Effect of post-annealing temperature on the alumina coating of LiNi0.5Mn1.5O4 cathode material

Spinel LiNi0.5Mn1.5O4 is considered as one of the most promising cathode materials due to high working voltage and high energy density. However, the fast capacity degradation, mainly induced by the instability of electrode/electrolyte interface and bulk structure, heavily prevents its commercial application. To alleviate above two issues, LiNi0.5Mn1.5O4 material was first coated with Al(OH)3 via double hydrolysis reactions between NaAlO2 and AlCl3·6H2O, where the corrosion of LiNi0.5Mn1.5O4 material is avoided by controlling the feeding sequence, and the uniform coating of Al(OH)3 on particle surface is achieved by controlling the feeding rate. The Al(OH)3-coated LiNi0.5Mn1.5O4 material was post-annealed at different temperatures, and the effects of different post-annealing temperatures on the structure, morphology and electrochemical performance of LiNi0.5Mn1.5O4 material were systematically investigated. It is found that the LiNi0.5Mn1.5O4 material after post-annealing treatment at 600 ​°C exhibits the optimal rate and cycling performances, which can be mainly attributed to the synergistic effect of Al2O3 surface coating and doping. The uniform and thin Al2O3 coating layer can avoid the direct contact of electrode with electrolyte, capture corrosive HF and increase oxygen vacancy on particle surface, while Al3+ doping can eliminate LixNi1-xO impurity phase, reduce Mn3+ content, strengthen the spinel structure and make Li+ ions diffusion easier, thus leading to the simultaneous improvement of interfacial and structural stability of LiNi0.5Mn1.5O4 material.

Scalable synthesis of high-voltage LiNi0.5Mn1.5O4 with high electrochemical performances by a modified solid-state method for lithium ion batteries

Spinel LiNi0.5Mn1.5O4 is promising for next-generation lithium-ion batteries, owing to its high-voltage, low-cost, and non-toxicity. However, undesirable impurities (such as LixNi1−xO or NiO) were introduced when it was synthesized by conventional solid-state methods, due to incomplete mixing of reactants, resulting in poor performances. Here, a formic-acid-pretreated solid-state method was proposed to address this issue by adding an environmental-friendly pretreatment process to the conventional methods. Atomic-levelmixing of Li, Ni, and Mn in the precursor was achieved, thereby promoting the formation of pure LiNi0.5Mn1.5O4. The initial discharge capacity was 130.6 mAh g−1, approaching its theoretical value (147 mAh g−1). Correspondingly, 91.4% of the initial capacity was maintained after 300 cycles under 0.3C, showing long-term stability. Besides, the capacity was 99.9 mAh g−1 (76.5% of that at 0.3C) at 20C, indicating excellent rate performance. They suggest the effectiveness of our method, which promotes the development of next-generation Li-ion batteries.

Facile synthesis of spinel LiNi0.5Mn1.5O4 as 5.0 V-class high-voltage cathode materials for Li-ion batteries

LiNi0.5Mn1.5O4 and LiMn2O4 with novel spinel morphology were synthesized by a hydrothermal and post-calcination process. The synthesized LiMn2O4 particles (5–10 μm) are uniform hexahedron, while the LiNi0.5Mn1.5O4 has spindle-like morphology with the long axis 10–15 μm, short axis 5–8 μm. Both LiMn2O4 and LiNi0.5Mn1.5O4 show high capacity when used as cathode materials for Li-ion batteries. In the voltage range of 2.5–5.5 V at room temperature, the LiNi0.5Mn1.5O4 has a high discharge capacity of 135.04 mA⋅h⋅g−1 at 20 mA⋅g−1, which is close to 147 mA⋅h⋅g−1 (theoretical capacity of LiNi0.5Mn1.5O4). The discharge capacity of LiMn2O4 is 131.08 mA⋅h⋅g−1 at 20 mA⋅g−1. Moreover, the LiNi0.5Mn1.5O4 shows a higher capacity retention (76%) compared to that of LiMn2O4 (61%) after 50 cycles. The morphology and structure of LiMn2O4 and LiNi0.5Mn1.5O4 are well kept even after cycling as demonstrated by SEM and XRD on cycled LiMn2O4 and LiNi0.5Mn1.5O4 electrodes.

Improving Electrochemical Performance of High-Voltage Spinel LiNi0.5Mn1.5O4 Cathodes by Silicon Oxide Surface Modification

Improving Electrochemical Performance of High-Voltage Spinel LiNi_0.5Mn_1.5O₄ Cathodes by Silicon Oxide Surface Modification

Suppressed phase separation in spinel LiNi0.5Mn1.5O4 cathode via interstitial sites modulation

Spinel LiNi0.5Mn1.5O4 (LNMO) is widely utilized because of its high-energy-density and high-voltage. Unfortunately, there is still much research to be done for LNMO due to its poor structural stability. Here, a strategy is confirmed to stabilize LNMO via modulating interstitial sites. The interstitial 16c sites of the octahedron are partially occupied by Ni2+ to suppress the migration and dissolution of manganese ions upon electrochemical cycling and stabilize lithium-ion vacancies in the state of charge. Unexpectedly, this protocol not only suppresses the phase separation restraining the phase boundary dislocations and stress but also decreases the magnitude of cell volume change during cycling, which originates from the change in Ni redox couple energy states. This two-pronged modification strategy endows the cathode material with a lower charge transfer barrier and faster Li+ transfer kinetics, revealing superior electrochemical performance. The regulated cathode material remains robust after 900 cycles at 1C and its capacity retention rate is 29% higher than that of the original sample. Our research is useful for providing a concrete example of how the electrochemical performance of spinel LNMO and other high voltage cathode materials can be enhanced.

Reactivity of LiNi0.5Mn1.5O4 in (Acidic) Water and Impact on the Electrochemical Performance

As the world-wide demand for Li-ion batteries (LIBs) is continuously rising, the efforts to make the production of LIBs more sustainable are rapidly increasing as well.[1] Given that aqueous processing has already become the standard for the negative electrode, adapting also the processing of the positive electrode to water-based fabrication routes would eventually allow for completely eliminating the use of harmful N-methyl-2-pyrrolidone (NMP). In addition to the beneficial impact on sustainability and environmental friendliness, the use of water would enable avoiding the need for the complex NMP recovery and, thus, also result in lower costs for the electrode manufacturing.[2] However, the contact of commonly used oxide-type cathode materials with water leads to undesired side reactions, where amongst others LiOH and Li2CO3 form on the particle surface. Previous studies have shown that the immediate negative impact of LiOH, i.e., the rise of the slurry pH level, can be mitigated by the addition of phosphoric acid during processing to prevent the corrosion of the Al current collector.[3 , 4] While this strategy has proven viable for enabling the aqueous electrode manufacturing of all kinds of Li-ion positive electrode materials,[5] we are herein elucidating the direct impact of aqueous and (phosphoric) acidic treatments on the high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) active material itself prior to the slurry preparation. Our extensive structural investigations using a comprehensive set of complementary techniques revealed that the water and acid treatment did not evoke any changes in the bulk material. On the material surface, however, a variety of different species is formed – some with a beneficial effect on the electrochemical performance (e.g., Li3PO4), some with a detrimental impact (e.g., Li2CO3 and transition metal carbonates). Nevertheless, the careful adjustment of the (acidic) aqueous treatment eventually results in a capacity retention of 95% after 500 cycles – clearly outperforming the NMP-processed reference.

Doped High Voltage Spinel for High Energy Cathode

High voltage spinel LiNi0.5Mn1.5O4 (LNMO) is a promising cathode material due to its Co-free nature, high operating voltage and high ionic conductivity. However, the rapid capacity fading, especially at high temperature, limits its commercial success. The root causes of this limitation are the dissolution of transition metals of Ni/Mn in the electrolyte and unstable crystal structure. Doping with other elements is a prevalent strategy to effectively improve the electrochemical performance of LNMO cathode. In this study, precursors doped with Ca and Sr were synthesized through a co-precipitation process and the doped LNMO was achieved by high temperature sintering precursors with lithium sources. The doping level in final LNMO products was controlled through adjusting the ratio of elements in the precursor solutions. Analysis on X-ray diffraction (XRD) showed that Ca and Sr were successfully incorporated into the LNMO crystal structure. The Rietveld refinement was used to further reveal the doping sites. The obtained products were evaluated as cathodes of lithium-ion batteries (LIBs). Compared to baseline undoped LNMO, doped cathodes delivered slightly lower capacity, but exhibited improved durability at room temperature and high temperature of 55 °C. Post-mortem analysis revealed that integrity of crystal structure was well preserved in doped LNMO after numerous cycles. It is believed that the improved electrochemical performance is ascribed to the strong affinity of Ca2+ and Sr2+ to oxygen, which could effectively alleviate the dissolution of Ni/Mn and stabilize the crystal structure. The effect of doping level on the electrochemical performance of LNMO was also investigated.

Synergistic effect of Mg and Y co-dopants on enhancement of electrochemical properties of LiNi0.5Mn1.5O4 spinel

The LiNi0.5–xMgxMn1.48Y0.02O4 (x = 0.005, 0.01, 0.03) and LiNi0.5Mn1.5O4 (LNMO) cathode materials were synthesized successfully through a citric acid aided route. The relationship between material characteristics (structure and morphology) and electrochemical properties of LNMO cathode materials was investigated. It was found that synergistic effect of co-doped magnesium and yttrium ions resulted in marked enhancement of electrochemical properties of LNMO cathode. SEM observation showed that Mg-Y co-doped samples possessed spinel structure with truncated octahedron morphology. After co-doping Mg and Y, the XRD and TEM analyses showed that lattice parameters for LNMO samples were improved, thus improving the rate and cycling property. XPS results of Mg-Y co-doped spinel LiNi0.5Mn1.5O4 indicated the presence of Mg2+ and Y3+ in the spinel lattice. Notably, LiNi0.49Mg0.01Mn1.48Y0.02O4 exhibited both optimal cycling stability and rate performance. LiNi0.49Mg0.01Mn1.48Y0.02O4 sample retained specific capacity of 131 mAh g−1 after 100 cycles at high current density of 1 C with superior retention of 98.49% and the specific capacity reached 118 mAh g−1 at 5 C. While undoped sample only retained 107 mAh g−1 after 100 cycles at 1 C with lower retention of 94.69% and its specific capacity was 84 mAh g−1 at 5 C.

Variation of Li Diffusion Coefficient during Delithiation of Spinel LiNi0.5Mn1.5O4

For this study, the sol gel method was used to synthesize the spinel LiNi0.5Mn1.5O4 (LNMO) electrode material. Structural, morphological, electrochemical, and kinetic aspects of the LNMO have been characterized. The synthesized LNMO was indexed with the Fd3̄m cubic space group. The excellent capacity retention indicates that the spinel framework of LNMO has the ability to withstand high rate charge-discharge throughout long cycle tests. The Li diffusion coefficient (DLi) changes non-monotonically across three orders of magnitude, from 10−9 to 10−12 cm2 s−1 determined from GITT method. The variation of DLi seemed to be related to three oxidation reactions that happened throughout the charging process. A small dip in DLi at the beginning stage of Li deintercalation is correlated with the oxidation of Mn3+ to Mn4+. While two pronounced DLi minima at 4.7 V and 4.75 V are due to the oxidation of Ni2+/Ni3+ and Ni3+/Ni4+ respectively. The depletion of DLi at the high voltage region is attributed to the occurrence of two successive phase transformation phenomena.

HEPES-Assisted Co-Precipitation Synthesis of LiNi0.5Mn1.5O4: Tuning the Mn3+ Content and Electrochemical Properties by pH Values

Spinel LiNi0.5Mn1.5O4 material (LNMO) is now actively developed as a promising cathode for next generation lithium-ion batteries due to its high specific energy, high rate capability, high operating potential, and low cost. However, its performance degradation originating from transition metal dissolution and severe side reactions remains a critical challenge. Herein, a new solution system 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid (HEPES) buffer solution for the synthesis of the spinel LiNi0.5Mn1.5O4 material is reported, which is not only the pH stabilizer, but also the chelating agent. The obtained LNMO exhibits excellent electrochemical performance, and its capacity retention is kept as 95.8%, and 88.9% after cycled at 5 C and 10 C for 1000 times, respectively. These can be attributed to homogenous distributions of elements in the as-prepared carbonate precursors, stable pH value of reaction base solution and suitable Mn3+ content in pure LNMO.

Long-life LiNi0.5Mn1.5O4/graphite lithium-ion cells with an artificial graphite-electrolyte interface

The high operating voltage of a spinel LiNi0.5Mn1.5O4 (LNMO) cathode leads to electrolyte decomposition and accelerated deterioration of the electrode/electrolyte interface in lithium-ion cells. Aggressive side reactions prevent long-term cycling and hinder its practical application. Advanced characterization shows that the high-voltage operation makes the graphite anode react with the electrolyte, particularly with the lithium salt in the electrolyte, resulting in massive active lithium inventory loss and capacity fade. The side reactions at the graphite are identified as the main culprit for the LNMO/graphite full cell decay. Here, we demonstrate that an artificial solid-electrolyte interface layer consisting of an ultra-thin Al2O3 film, generated via atomic layer deposition (ALD) at the graphite surface, can successfully isolate the graphite from the electrolyte and inhibit the undesired reactions. Consequently, the capacity and cycling stability of the LNMO/graphite cell are drastically improved. After 300 cycles, the capacity retention of LNMO/graphite cell increases from 57.7% to 98.6% with the ALD-coated graphite. Our findings provide valuable insights into the LNMO/graphite cell degradation and suggest a simple and robust, yet highly effective, approach for the practical viability of high-voltage lithium-ion batteries.

Structural, electrical and electrochemical characterization of hybrid morphological LiNi0.5Mn1.5O4 cathode material

Spinel LiNi0.5Mn1.5O4 (LNMO) cathode are effectively obtained by one-pot hydrothermal synthesis. Scanning electron microscopy (SEM) reveals the hybrid morphological of LNMO, featuring cotton-like structures (400–800 nm) and rod-like structures (90–150 nm). The equivalent circuit well describes the Nyquist plot to separate the grain and grain boundary effects. According to the Maxwell-Wagner model, the complex permittivity confirms non-homogenous layers' existence; highly conducting grains and poorly conducting grain boundaries. Non-overlapping polar tunneling (NSPT) and correlated barrier hopping (CBH) are two responsible models for the conduction mechanism at low and high temperatures. Further, identical activation energy values are observed for hopping frequency, and peak frequency from normalized parameters Z’’/Z’’ max and M’’/M’’ max, suggesting Li+ ions are the dominant charge carriers. The LNMO/Li cell delivers higher discharge capacity than commercial LNMO/Li cell from prior study, credits from the bridging features between rod-like and cotton-like particles.

Spinel LiNi0.5Mn1.5O4 with ultra-thin Al2O3 coating for Li-ion batteries: investigation of improved cycling performance at elevated temperature

Spinel LiNi0.5Mn1.5O4 with ultra-thin Al2O3 coating for Li-ion batteries: investigation of improved cycling performance at elevated temperature

Bioinspired PDA@TiO2 modification on high-voltage LiNi0.5Mn1.5O4 toward enhancing electrochemical performance

Improving the cycling performance without sacrificing its capacity is challenging for high-voltage LiNi0.5Mn1.5O4 cathode due to the trade-off nature among the key properties. A self-polymerization process of dopamine was utilized to grow polydopamine (PDA)-nano titanium dioxide assembly. PDA@TiO2 composite was demonstrated to be integrated with the particles of high-voltage spinel LiNi0.5Mn1.5O4 cathodes via wet chemical method. PDA@TiO2 decorated LNMO improved the long-term cycling performance and rate capability by suppressing detrimental side reactions in balancing the interfacial stability and Li+ diffusion kinetics of LNMO and consequently providing efficient conductive pathways. As a result, 2% PDA@TiO2 modified LNMO cathode exhibited the high reversible capacity of 117mAhg−1 after 1000 cycles with good capacity retention of 90.7% at 1 C, and superior rate capability (78.5mAhg−1 at 5 C) at room temperature. Remarkably, a significant improvement in cycling stability at an elevated temperature (50°C) was obtained for the PDA@TiO2-LNMO composite, giving a capacity retention of 93% after 100 cycles at 1 C. The mechanism of performance improvement could be attributed to the maintenance of the structural stability of LNMO cathode materials and the enhanced kinetics of the remarkable lithium-ion diffusion through the protective effect of PDA@TiO2 decorating.