Facile preparation of core@shell and concentration-gradient spinel particles for Li-ion battery cathode materials

Abstract

Core@shell and concentration-gradient particles have attracted much attention as improved cathodes for Li-ion batteries (LIBs). However, most of their preparation routes have employed a precisely-controlled co-precipitation method. Here, we report a facile preparation route of core@shell and concentration-gradient spinel particles by dry powder processing. The core@shell particles composed of the MnO₂ core and the Li(Ni,Mn)₂O₄ spinel shell are prepared by mechanical treatment using an attrition-type mill, whereas the concentration-gradient spinel particles with an average composition of LiNi_0.32Mn_1.68O₄ are produced by calcination of their core@shell particles as a precursor. The concentration-gradient LiNi_0.32Mn_1.68O₄ spinel cathode exhibits the high discharge capacity of 135.3 mA h g^?1, the wide-range plateau at a high voltage of 4.7 V and the cyclability with a capacity retention of 99.4% after 20 cycles. Thus, the facile preparation route of the core@shell and concentration-gradient particles may provide a new opportunity for the discovery and investigation of functional materials as well as for the cathode materials for LIBs.     

In Situ Formation of a Cathode–Electrolyte Interface with Enhanced Stability by Titanium Substitution for High Voltage Spinel Lithium‐Ion Batteries

Although LiNi_0.5Mn_1.5O₄ (LNMO) high‐voltage spinel is a promising candidate for a next generation cathode material, LNMO/graphite full cells experience severe capacity fading caused by degradation reactions at electrode/electrolyte interfaces and consequent active Li⁺ loss in the cells. In this study, it is first reported that in situ formation of a Ti–O enriched cathode/electrolyte interfacial (CEI) layer on a Ti‐substituted LiNi_0.5Mn_1.2Ti_0.3O₄ (LNMTO) spinel cathode effectively mitigates electrolyte oxidation and transition metal dissolution, which improves the Coulombic efficiency and cycle life of LNMTO/graphite full cells. The Ti–O enriched CEI layer is produced in situ during an initial cycling of LNMTO as a result of selective Mn and Ni dissolution at its surface, as evidenced by various surface characterizations using X‐ray photoelectron spectroscopy, transmission electron microscopy, time‐of‐flight secondary ion mass spectrometry, Raman spectroscopy, and synchrotron‐based soft X‐ray absorption spectroscopy. The Ti–O enriched CEI has an advantage over traditional LNMO powder coatings, namely the formation of conformal CEI without compromising electronic conduction pathways between cathode particles.     

Post-doping via spray-drying: a novel sol–gel process for the batch synthesis of doped LiNi0.5Mn1.5O4 spinel material

Powder granulation, Ti-doping and thermal post-treatment have beneficial effects on the electrochemical performance of 5 V LiNi_0.5Mn_1.5O₄ (LNMO) spinel materials. It is shown that spray-drying combined with a post-doping process step is suitable to prepare Ti-doped 5 V materials with a defined and highly reproducible microstructure and chemical composition. Powder granulation via spray-drying and thermal post-treatment provides spherical LNMO granules with nano-crystalline primary particles and a 10 % higher specific discharge capacity compared to pristine LNMO materials due to the presence of the partially ordered P4 ₃ 32 spinel phase and the reduced Mn³⁺ content. Powder granulation combined with a post-doping process step which utilizes titanium containing sol leads to spherical LiNi_0.5Mn_1.47Ti_0.03O₄ granules with uniform nano-crystalline primary particles and a homogenous Ti distribution. The second calcination process after spray-drying as well as the Ti-doping cause a reduced content of the Li _x Ni_1?x O impurity phase. This facile sol–gel processing leads to doped LiNi_0.5Mn_1.47Ti_0.03O₄ with an increased discharge capacity of 18 % compared to the original material. All the granulated materials show a good rate performance up to 10 C due to their particular microstructure.     

LiNi0.5Mn1.5O4 cathode material by low-temperature solid-state method with excellent cycleability in lithium ion battery

LiNi_0.5Mn_1.5O₄ cathode material was synthesized from a mixture of LiCl, NiCl₂?6H₂O and MnCl₂?4H₂O with 70 wt.% oxalic acid by a low-temperature solid-state method. The calcination temperature was adjusted to form disorder Fd3m structure at 700-800 °C for 10 h.XRD patterns and FTIR spectroscopy showed that the LiNi_0.5Mn_1.5O₄ cathode material exhibited an impurity-free spinel Fd3m structure. Electrochemical property results revealed that the LiNi_0.5Mn_1.5O₄ cathode material charged at 1C rate to 4.9 V and discharged at 2 and 3 C to 3.5 V delivered initial capacity of 120 mAh/g and maintained a capacity retention over 80% at room temperature after 1000 charge/discharge cycles.     

Multi-shelled porous LiNi0.5Mn1.5O4 microspheres as a 5 V cathode material for lithium-ion batteries

Multi-shelled porous LiNi_0.5Mn_1.5O₄ microspheres have been successfully synthesized by a co-precipitation approach combined with high-temperature calcinations. The compositions and structures of multi-shelled LiNi_0.5Mn_1.5O₄ microspheres have been investigated by a variety of characterization methods. The LiNi_0.5Mn_1.5O₄ microspheres are composed of a lot of concentric circular porous shells with constant O, Mn, and Ni concentration, which is ascribed to the fast outward diffusion of Mn and Ni atoms and the slow inward diffusion of O and Li atoms during the calcination process. Electrochemical measurements show that LiNi_0.5Mn_1.5O₄ microspheres deliver good cycling stability and rate capability with discharge capacities of 137.1 (0.1 C), 133.9 (0.2 C), 124.2 (0.5 C), 114.9 (1 C), and 96.0 mAh g⁻¹ (2 C). The LiNi_0.5Mn_1.5O₄ microspheres synthesized by the facile method may be a promising cathode candidate for high energy density lithium-ion batteries.     

Carbon‐Coated Li3VO4 Spheres as Constituents of an Advanced Anode Material for High‐Rate Long‐Life Lithium‐Ion Batteries

Lithium‐ion batteries are receiving considerable attention for large‐scale energy‐storage systems. However, to date the current cathode/anode system cannot satisfy safety, cost, and performance requirements for such applications. Here, a lithium‐ion full battery based on the combination of a Li₃VO₄ anode with a LiNi_0.5Mn_1.5O₄ cathode is reported, which displays a better performance than existing systems. Carbon‐coated Li₃VO₄ spheres comprising nanoscale carbon‐coating primary particles are synthesized by a morphology‐inheritance route. The observed high capacity combined with excellent sample stability and high rate capability of carbon‐coated Li₃VO₄ spheres is superior to other insertion anode materials. A high‐performance full lithium‐ion battery is fabricated by using the carbon‐coated Li₃VO₄ spheres as the anode and LiNi_0.5Mn_1.5O₄ spheres as the cathode; such a cell shows an estimated practical energy density of 205 W h kg^?1 with greatly improved properties such as pronounced long‐term cyclability, and rapid charge and discharge.     

Low temperature synthesis of LiNi0.5Mn1.5O4 spinel

Pure LiNi_0.5Mn_1.5O₄ phase was prepared by one-step solid-state reaction at 600 °C in air. TG measurement revealed that the oxygen loss occurred when the mixed precursors were heated above 700 °C. X-ray diffraction (XRD) pattern and scanning electron microscopic (SEM) image indicated that LiNi_0.5Mn_1.5O₄ has cubic spinel structure with small and homogeneous particles. Electrochemical test showed that the prepared LiNi_0.5Mn_1.5O₄ delivered up to 138 mA h g^− 1, and the capacity retained 128 mA h g^− 1 after 30 cycles.     

Recent breakthroughs and perspectives of high-energy layered oxide cathode materials for lithium ion batteries

Ni-rich layered oxides (NRLOs) and Li-rich layered oxides (LRLOs) have been considered as promising next-generation cathode materials for lithium ion batteries (LIBs) due to their high energy density, low cost, and environmental friendliness. However, these two layered oxides suffer from similar problems like capacity fading and different obstacles such as thermal runaway for NRLOs and voltage decay for LRLOs. Understanding the similarities and differences of their challenges and strategies at multiple scales plays a paramount role in the cathode development of advanced LIBs. Herein, we provide a comprehensive review of state-of-the-art progress made in NRLOs and LRLOs based on multi-scale insights into electrons/ions, crystals, particles, electrodes and cells. For NRLOs, issues like structure disorder, cracks, interfacial degradation and thermal runaway are elaborately discussed. Superexchange interaction and magnetic frustration are blamed for structure disorder while strains induced by universal structural collapse result in issues like cracks. For LRLOs, we present an overview of the origin of high capacity followed by local crystal structure, and the root of voltage hysteresis/decay, which are ascribed to reduced valence of transition metal ions, phase transformation, strains, and microstructure degradation. We then discuss failure mechanism in full cells with NRLO cathode and commercial challenges of LRLOs. Moreover, strategies to improve the performance of NRLOs and LRLOs from different scales such as ion-doping, microstructure designs, particle modifications, and electrode/electrolyte interface engineering are summarized. Dopants like Na, Mg and Zr, delicate gradient concentration design, coatings like spinel LiNi_0.5Mn_1.5O₄ or Li₃PO₄ and novel electrolyte formulas are highly desired. Developing single crystals for NRLOs and new crystallographic structure or heterostructure for LRLOs are also emphasized. Finally, remaining challenges and perspectives are outlined for the development of NRLOs and LRLOs. This review offers fundamental understanding and future perspectives towards high-performance cathodes for next-generation LIBs.     

Surface morphology,elastic modulus and hardness of thin film cathodes for Li-ion rechargeable batteries

In this study, surface morphology, elastic modulus and hardness of two thin film cathode materials, namely layered structured LiNi_1/3Co_1/3Mn_1/3O₂ and spinel structured LiMn₂O₄, during the charge/discharge cycles, are measured by using Scanning Electron Microscopy, Atomic Force Microscopy and nanoindentation experiments. Furthermore, the effects of depth of discharge (DOD) and charging rate (current density) on the changes of elastic modulus and hardness of the spinel structured LiMn₂O₄ are also investigated. The results have shown that both elastic modulus and hardness of the thin film cathodes have been significantly affected by the charge/discharge cycles as well as the condition of the charge/discharge processes. These results suggest the importance of the mechanical properties of the cathode materials to the reliability and integrity of the cathode materials to be used for the Li-ion batteries. The possible mechanisms of the changes in mechanical properties are also discussed.     

Rapid synthetic routes to prepare LiNi1/3Mn1/3Co1/3O2 as a high voltage, high-capacity Li-ion battery cathode material

LiNi_1/3Mn_1/3Co_1/3O₂, a high voltage and high-capacity cathode material for Li-ion batteries, has been synthesized by three different rapid synthetic methods, viz. nitrate-melt decomposition, combustion and sol–gel methods. The first two methods are ultra rapid and a time period as small as 15 min is sufficient to prepare nano-crystalline LiNi_1/3Mn_1/3Co_1/3O₂. The processing parameters in obtaining the best performing materials are optimized for each process and their electrochemical performance is evaluated in Li-ion cells. The combustion-derived LiNi_1/3Mn_1/3Co_1/3O₂ sample exhibits large extent of cation mixing (10%) while the other two methods yield LiNi_1/3Mn_1/3Co_1/3O₂ with cation mixing <5%. LiNi_1/3Mn_1/3Co_1/3O₂ prepared by nitrate-melt decomposition method exhibits superior performance as Li-ion battery cathode material.     

Nanoscale Manipulation of Spinel Lithium Nickel Manganese Oxide Surface by Multisite Ti Occupation as High‐Performance Cathode

A novel two‐step surface modification method that includes atomic layer deposition (ALD) of TiO₂ followed by post‐annealing treatment on spinel LiNi_0.5Mn_1.5O₄ (LNMO) cathode material is developed to optimize the performance. The performance improvement can be attributed to the formation of a TiMn₂O₄ (TMO)‐like spinel phase resulting from the reaction of TiO₂ with the surface LNMO. The Ti incorporation into the tetrahedral sites helps to combat the impedance growth that stems from continuous irreversible structural transition. The TMO‐like spinel phase also alleviates the electrolyte decomposition during electrochemical cycling. 25 ALD cycles of TiO₂ growth are found to be the optimized parameter toward capacity, Coulombic efficiency, stability, and rate capability enhancement. A detailed understanding of this surface modification mechanism has been demonstrated. This work provides a new insight into the atomic‐scale surface structural modification using ALD and post‐treatment, which is of great importance for the future design of cathode materials.     

A new strategy to diminish the 4 V voltage plateau of LiNi0.5Mn1.5O4

As for spinel LiNi_0.5Mn_1.5O₄, there is 4 V voltage plateau in the charge–discharge profiles. This voltage plateau can be reduced by an annealing process, however it is hard to avoid it completely. In this study, a new strategy of partial substitution for Mn by Mg is applied. There is no 4 V voltage plateau in the charge–discharge profiles of Mg-doped compound LiNi_0.5Mn_1.45Mg_0.05O₄. This compound exhibits good electrochemical properties which can be used as cathode material of lithium ion batteries. At 1 C rate, it can deliver a capacity of around 129 mAh g⁻¹ and remain good cycle performance.     

Fluorine-doped LiNi0.5Mn1.5O4 for 5 V cathode materials of lithium-ion battery

Fluorine-doped 5 V cathode materials LiNi_0.5Mn_1.5O_4−xF_x (0.05 ≤ x ≤ 0.2) have been prepared by sol-gel and post-annealing treatment method. The results from X-ray diffraction and scanning electron microscopy (SEM) indicate that the spinel structure changes little after fluorine doping, but the particle size varies with fluorine doping and the preparation conditions. The electrochemical measurements show that stable cycling performance can be obtained when the fluorine amount x is higher than 0.1, but the specific capacity is decreased and 4 V plateau capacity resulting from a conversion of Mn⁴⁺/Mn³⁺ remains. Moreover, influence of the particle size on the reversible capacity of the electrode, especially on the kinetic property, has been examined.     

Electrochemical performance and thermal stability of GaF3-coated LiNi0.5Mn1.5O4 as 5 V cathode materials for lithium ion batteries

LiNi_0.5Mn_1.5O₄ coated with various amounts of GaF₃ were prepared and investigated as cathode materials for lithium ion batteries. The sample was characterized by X-ray diffraction, transmission electron microscopy, and energy-dispersive X-ray spectroscopy (EDX). The results indicated that the electrochemical performance of LiNi_0.5Mn_1.5O₄ was effectively improved by the GaF₃ coating. The 0.5 wt% GaF₃-coated LiNi_0.5Mn_1.5O₄ delivered a discharge capacity of 97 mAh g^?1 at 20 C (3000 mA g^?1), while the pristine sample only yielded 80 mAh g^?1 at 10 C. Meanwhile, the 0.5 wt% GaF₃-coated LiNi_0.5Mn_1.5O₄ exhibited an obviously better cycle life than the bare sample at 60 °C, delivering a discharge capacity of 120.4 mAh g^?1 after 300 cycles, 82.9 % of its initial discharge capacity, while the pristine only gave 75 mAh g^?1. At 0.1 C, the self-discharge of 0.5 wt% GaF₃-coated LiNi_0.5Mn_1.5O₄ is about 3.4 %, while the pristine is about 10.2 % after a 5-day rest at room temperature. Furthermore, GaF₃ coating greatly reduced the self-heating rate and improved the thermal stability of LiNi_0.5Mn_1.5O₄. These improvements were attributed to the GaF₃ layer not only increasing the electronic conductivity of the LiNi_0.5Mn_1.5O₄ but also effectively suppressing the reaction between the LiNi_0.5Mn_1.5O₄ and the electrolytes, which reduced the charge-transfer impedance and the dissolution of Ni and Mn during cycling.     

Regulating Surface and Grain‐Boundary Structures of Ni‐Rich Layered Cathodes for Ultrahigh Cycle Stability

The wide applications of Ni‐rich LiNi_1‐x‐yCo_xMn_yO₂ cathodes are severely limited by capacity fading and voltage fading during the cycling process resulting from the pulverization of particles, interfacial side reactions, and phase transformation. The canonical surface modification approach can improve the stability to a certain extent; however, it fails to resolve the key bottlenecks. The preparation of Li(Ni_0.4Co_0.2Mn_0.4)_1‐xTi_xO₂ on the surface of LiNi_0.8Co_0.1Mn_0.1O₂ particles with a coprecipitation method is reported. After sintering, Ti diffuses into the interior and mainly distributes along surface and grain boundaries. A strong surface and grain boundary strengthening are simultaneously achieved. The pristine particles are fully pulverized into first particles due to mechanical instability and high strains, which results in serious capacity fading. In contrast, the strong surface and the grain boundary strengthening can maintain the structural integrity, and therefore significantly improve the cycle stability. A general and simple strategy for the design of high‐performance Ni‐rich LiNi_1‐x‐yCo_xMn_yO₂ cathode is provided and is applicable to surface modification and grain‐boundary regulation of other advanced cathodes for batteries.     

Converting Nafion into Li+-Conductive Nanoporous Materials

Sulfonated polymers have long been used as proton-conducting materials in fuel cells, and their ionic transport features are highly attractive for electrolytes in lithium-ion/metal batteries (LIBs/LMBs). However, most studies are still based on a preconceived notion of using them directly as polymeric ionic carriers, which precludes exploring them as nanoporous media to construct efficient lithium ions (Li⁺) transport network. Here, effective Li⁺-conducting channels realized by swelling nanofibrous Nafion is demonstrated, which is a classical sulfonated polymer in fuel cells. The sulfonic acid groups, interact with LIBs liquid electrolytes to form porous ionic matrix of Nafion and assist partial desolvation of Li⁺-solvates to further enhance Li⁺ transport. Li-symmetric cells and Li-metal full cells (Li₄Ti₅O₁₂ or high-voltage LiNi_0.6Co_0.2Mn_0.2O₂ as a cathode) with such membrane show excellent cycling performance and stabilized Li-metal anode. The finding provides a strategy to convert the vast sulfonated polymer family into efficient Li⁺ electrolyte, promoting the development of high-energy–density LMBs.     

Recent progress on nanostructured 4 V cathode materials for Li-ion batteries for mobile electronics

Mobile electronics have developed so rapidly that battery technology has hardly been able to keep pace. The increasing desire for lighter and thinner Li-ion batteries with higher capacities is a continuing and constant goal for in research. Achieving higher energy densities, which is mainly dependent on cathode materials, has become a critical issue in the development of new Li-ion batteries. In this review, we will outline the progress on nanostructured 4 V cathode materials of Li-ion batteries for mobile electronics, covering LiCoO₂, LiNi_xCo_yMn_1?x?yO₂, LiMn₂O₄, LiNi_0.5Mn_1.5O₄ and Li-rich layered oxide materials. We aim to provide some scientific insights into the development of superior cathode materials by discussing the advantages of nanostructure, surface-coating, and other key properties.     

Facile synthesis,characterization and BET study of neodymium-doped spinel Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> nanomaterial with enhanced photocatalytic activity

In this study, bare Mn₃O₄ and Neodymium (Nd)-doped Mn₃O₄ were prepared via a facile hydrothermal strategy. These materials were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, UV spectroscopy, X-ray photoelectron spectroscopy, and the Brunauer–Emmett–Teller (BET) method. XRD pattern displays that the particles were well crystallized and corresponds to a spinel structure of Mn₃O₄. The BET specific surface area and pore volume of mesoporous Mn₃O₄ greatly exceeds that of Nd-doped Mn₃O₄ samples. The sonophotocatalytic activity of Nd-doped Mn₃O₄ nanoparticles was evaluated by monitoring the decolorization of Reactive Red 43 in aqueous solution under sono-photocatalytic process. 4% Nd-doped Mn₃O₄ nanoparticles showed the highest decolorization efficiency among the different amounts of dopant agent used. The Nd-doped Mn₃O₄ could be a promising candidate material for high-capacity, low-cost, and environmentally friendly catalyst for wastewater remediation.     

Ce-modified LiNi0.5Co0.2Mn0.3O2 cathode with enhanced surface and structural stability for Li ion batteries

The well-established LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) cathode materials possess a broad prospect for Li-ion batteries. However, the NCM523 still suffers severe capacity fading and structural instability. In this research, Ce-doped and CeO₂-coated NCM523 cathode materials are synthesized by a smart one-step calcination process. It is found that the CeO₂ coating layer is formed during high-temperature calcination. The CeO₂ coating layers stop the electrode from being exposed to the electrolyte directly and promote the kinetics of lithium deintercalation. Besides, Ce doping could suppress the bulk cation-mixing degree. Electrochemical tests suggest that Ce-modification improves the capacity retention of cathode materials. The optimized Ce-modification cathode material, among 2.7 V and 4.6 V, not only shows the best capacity retention of 76.2%, but also delivers a discharge capacity of 178.2 mAh g^?1 at 1 C. This smart modification strategy provides novel ideas for advanced LIBs.     

Spinel LiNi0.5Mn1.5O4 cathode ion batteries： Nano vs micro,disordered phase （F4332） for rechargeable lithium- ordered phase （P433m）

Since the high-voltage spinel LiNi0.5Mn1504 （LNMO） is one of the most attractive cathode materials for lithium-ion batteries, how to improve the cycling and rate performance simultaneously has become a critical question. Nanosizing is a typical strategy to achieve high rate capability due to drastically shortened Li- ion diffusion distances. However, the high surface area of nanosized particles increases the side reaction with the electrolyte, which leads to poor cycling performance. Spinels with disordered structures could also lead to improved rate capability, but the cyclability is low due to the presence of Mn3＋ ions. Herein, we systematically investigated the synergic interaction between particle size and cation ordering. Our results indicated that a microsized disordered phase and a nanosized ordered phase of LNMO materials exhibited the best combination of high rate capability and cycling performance.