Ruizhi Yu

Suppressed capacity/voltage fading of high-capacity lithium-rich layered materials via the design of heterogeneous distribution in the composition

Lithium-rich layered materials, Li1+xM1−xO2 (M = Mn, Ni, Co), have been under intense investigation as high-performance cathode materials for lithium ion batteries due to their high discharge capacity, low cost and environmental benignity. Unfortunately, the practical uses of these oxides have so far been hindered by their severe capacity and voltage fading during high voltage cycling (>4.5 V vs. Li/Li+). In an attempt to overcome these problems, herein, a novel lithium-rich Li1.14[Mn0.60Ni0.25Co0.15]0.86O2 microsphere with heterogeneous distribution in the composition has been reasonably designed and successfully synthesized via a co-precipitation method. The chemical composition in the spherical particle is gradually altered by increasing the Mn concentration while reducing the Co content from the particle center to the outer layer. At the same time, the Ni content remains almost constant throughout the particle. The coin cell with the heterogeneous cathode material delivers a high discharge capacity of over 230 mA h g−1 between 2.0 V and 4.6 V, and shows excellent cyclic stability due to the continuous increase of the stable tetravalent Mn towards the outer surface of the spherical particles, corresponding to 93.8% capacity retention after 200 cycles at 0.5 C. More importantly, the as-prepared material exhibits a significantly lower discharge voltage decay compared with conventional materials, which may mainly be ascribed to the suppression of the layered-to-spinel transformation in the Co-rich/Mn-depleted regions of the spherical particle. The capacity and voltage fading of the lithium-rich layered material are simultaneously suppressed by the special architecturual design, and the results here will shed light on developing cathode materials with special structures and superior electrochemical properties for high-performance lithium ion batteries.

Facile synthesis and performances of nanosized Li2TiO3-based shell encapsulated LiMn1/3Ni1/3Co1/3O2 microspheres

LiMn1/3Ni1/3Co1/3O2 microspheres covered by a nanosized Li2TiO3-based shell are prepared by a facile synthesis method. First, a controllable TiO2 nano-layer is grown on the surface of a spherical Mn1/3Ni1/3Co1/3CO3 precursor, and then the resultant TiO2@LiMn1/3Ni1/3Co1/3O2 hybrid is synchronously transformed in situ into a hierarchical Li2TiO3@LiMn1/3Ni1/3Co1/3O2 microsphere through a solid-phase reaction. It has been found that the hierarchical Li2TiO3@LiMn1/3Ni1/3Co1/3O2 microspheres exhibit a good rate capability with a discharge capacity of 92.3 mA h g−1 even at higher rates of 20 C between 3.0 and 4.3 V. Besides, they possess excellent cyclic stability especially at high rates, with a capacity retention of 90.3% after 500 cycles at a 20 C rate. The enhanced electrochemical performance of the hierarchical Li2TiO3@LiMn1/3Ni1/3Co1/3O2 at high rates is attributed to the stable and fast Li+-conductor characteristic of the nanosized Li2TiO3-based shell. Thus, the Li2TiO3@LiMn1/3Ni1/3Co1/3O2 microspheres will be a promising cathode material for lithium-ion batteries with high power density and excellent cycling performance.

Effect of magnesium doping on properties of lithium-rich layered oxide cathodes based on a one-step co-precipitation strategy

A Mg-doped lithium-rich layered oxide material is successfully synthesized via a co-precipitation process and a subsequent high-temperature solid state method. The chemical composition, structural characteristics and elemental distribution of the Mg-doped lithium-rich layered oxide material are investigated by inductively coupled plasma optical emission spectroscopy (ICP-OES), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDXS). The results show that Mg is effectively and equably doped into the samples, which can replace partially Li+ in the cathode material. The electrochemical properties of the Mg-doped lithium-rich layered oxide material are evaluated and compared with those of the conventional Li1.5[Mn0.75Ni0.25]O2+δ cathode material. It can be found that the Mg-doped lithium-rich layered oxide material exhibits excellent electrochemical performance. It can deliver a high initial discharge capacity of 248.6 mA h g−1 and an improved initial coulombic efficiency of 87.9% at 0.1C with a cut-off voltage of 2.0–4.6 V. Moreover, the capacity retention reaches a relatively high value of 94.2% after 200 cycles at 0.5C. In contrast, the capacity retention of conventional Li1.5[Mn0.75Ni0.25]O2+δ is only 59.6%. In addition, the Mg-doped lithium-rich layered oxide material also shows excellent rate capability, which can display a discharge capacity of 130.1 mA h g−1 even at 10C and a capacity retention of 92.6% after 100 cycles at 5C. The enhanced electrochemical properties of the Mg-doped lithium-rich layered oxide material could be attributed to the introduction of Mg, which can effectively mitigate the structural deterioration of the material and facilitate the diffusion coefficient of Li+ during cycling.

Dependence of structure and temperature for lithium-rich layered-spinel microspheres cathode material of lithium ion batteries

Homogeneous lithium-rich layered-spinel 0.5Li2MnO3·0.5LiMn1/3Ni1/3Co1/3O2 microspheres (~1 μm) are successfully prepared by a solvothermal method and subsequent high-temperature calcinations process. The effects of temperature on the structure and performance of the as-prepared cathode material are systemically studied by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), galvanostatical charge/discharge and electrochemical impedance spectra. The results show that a spinel Li4Mn5O12 component can be controllably introduced into the lithium-rich layered material at 750°C. Besides, it has been found that the obtained layered-spinel cathode material represents excellent electrochemical characteristics. For example, it can deliver a high initial discharge capacity of 289.6 mAh g−1 between 2.0 V and 4.6 V at a rate of 0.1 C at room temperature, and a discharge capacity of 144.9 mAh g−1 at 5 C and 122.8 mAh g−1 even at 10 C. In addition, the retention of the capacity is still as high as 88% after 200 cycles, while only 79.9% for the single-phase layered material. The excellent electrochemical performance of the as-prepared cathode material can probably be attributed to the hybrid structures combining a fast Li-ion diffusion rate of 3D spinel Li4Mn5O12 phase and a high capacity of the layered Li-Mn-Ni-Co-O component.

Self-assembly synthesis and electrochemical performance of Li1.5Mn0.75Ni0.15Co0.10O2+δ microspheres with multilayer shells

Novel Li1.5Mn0.75Ni0.15Co0.10O2+δ microspheres with hierarchical multilayer shells were rationally designed and successfully prepared through a layer-by-layer self-assembly deposit with a co-precipitation process. The microsphere with multilayer shells consists of a Li1.5Mn0.75Ni0.25O2+δ inner core and hierarchical multilayer shells. The structure and electrochemical properties of the spherical Li1.5Mn0.75Ni0.15Co0.10O2+δ cathode material with multilayer shells are evaluated and compared to those of the conventional Li1.5Mn0.75Ni0.15Co0.10O2+δ cathode material with the same chemical composition as the multilayer spherical cathode material. The results show that the spherical cathode material with multilayer shells delivers a high discharge capacity of 257.8 mA h g−1 at a rate of 0.1 C with an outstanding capacity retention of 96.1% after 100 cycles at 0.5 C between 2.0 and 4.6 V. Especially, the spherical cathode material with multilayer shells exhibits an improved rate capability with a capacity of 102.7 mA h g−1 even at a high discharge rate of 10 C, and it is apparently superior to the conventional Li1.5Mn0.75Ni0.15Co0.10O2+δ cathode material (64.9 mA h g−1). Thus, the reasonable design for function and structure of cathode materials will be significant for improving the lithium ion battery performance.

Preparation and performance of 0.5Li2MnO3·0.5LiNi1/3Co1/3Mn1/3O2 with a fusiform porous micro-nano structure

A new lithium-rich layered cathode material 0.5Li2MnO3·0.5LiNi1/3Co1/3Mn1/3O2 with a porous fusiform micro-nano structure has been successfully synthesized via a facile co-precipitation method followed by high temperature calcination. X-ray diffraction (XRD), inductively coupled plasma optical emission spectroscopy (ICP-OES), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDXS) are used to characterize the chemical composition, structure, morphology and elemental distribution of the as-prepared lithium-rich layered material. It can be found that the as-prepared material presents a fusiform morphology and consists of interconnected nanosized subunits with a highly porous structure. The electrochemical measurements reveal that the material can deliver a high initial discharge capacity of 294.8 mA h g−1 and an excellent capacity retention of 87.1% after 200 cycles at 0.5C between 2.0 V and 4.6 V. In particular, even at a high rate of 10C, the material can still deliver a high discharge capacity of 139.5 mA h g−1. The excellent electrochemical performances can be ascribed to the unique fusiform porous micro-nano structure, which can facilitate the diffusion of lithium ions and enhance the structural stability of the lithium-rich layered cathode materials.

The effects of LiTi2(PO4)3 modification on the performance of spherical Li1.5Ni0.25Mn0.75O2+δ cathode material

The spherical layered Li1.5Ni0.25Mn0.75O2+δ cathode material is successfully modified with a LiTi2(PO4)3 (LTP) coating through a facile hydrothermal route. The effects of LTP modification on the structure, morphology and electrochemical performance of Li1.5Ni0.25Mn0.75O2+δ cathode material are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and charge–discharge tests. The results reveal that, among all the as-prepared samples, the sample modified with 3 wt% LTP delivers the highest reversible capacity of 254.9 mA h g−1 at 0.1C and excellent capacity retention of 95.8% after 100 cycles at 0.5C in a voltage range of 2–4.6 V. Additionally, the lithium-rich cathode material modified by LTP also exhibits superior rate capability with a capacity of 103.2 mA h g−1 even at a high discharge rate of 10C. The enhanced rate capability and cycling performances are attributed to the surface protective layer of LTP, which not only protects the surface of the active materials from electrolyte corrosion but also reduces the charge transfer resistance. Therefore, the modification with LTP of spherical lithium-rich cathode materials will be a promising technical route for the preparation of high performance lithium-ion battery cathode materials.

Li1.2Ni0.13Co0.13Mn0.54O2 with Controllable Morphology and Size for High Performance Lithium-Ion Batteries

The controllable morphology and size Li-rich Mn-based layered oxide Li1.2Ni0.13Co0.13Mn0.54O2 with micro/nano structure is successfully prepared through a simple coprecipitation route followed by subsequent annealing treatment process. By rationally regulating and controlling the volume ratio of ethylene glycol (EG) in hydroalcoholic solution, the morphology and size of the final products can be reasonably designed and tailored from rod-like to olive-like, and further evolved into shuttle-like with the assistance of surfactant. Further, the structures and electrochemical properties of the Li-rich layered oxide with various morphology and size are systematically investigated. The galvanostatic testing demonstrates that the electrochemical performances of lithium ion batteries (LIBs) are highly dependent on the morphology and size of Li1.2Ni0.13Co0.13Mn0.54O2 cathode materials. In particular, the olive-like morphology cathode material with suitable size exhibits much better electrochemical performances compared with the other two cathode materials in terms of initial reversible capacity (297.0 mAh g-1) and cycle performance (95.4% capacity retention after 100 cycles at 0.5 C), as well as rate capacity (142.8 mAh g-1 at 10 C). The excellent electrochemical performances of the as-prepared materials could be related to the synergistic effect of well-regulated morphology and appropriate size as well as their micro/nano structure.

Facile synthesis and performance of Na-doped porous lithium-rich cathodes for lithium ion batteries

Na-doped porous lithium-rich (Li-rich) cathode microspheres (∼1 μm) were firstly prepared via the solvothermal method and subsequently a high-temperature calcination process. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption–desorption isotherms were used to characterize the structure and morphology of the as-prepared cathode material. It has been found that the as-prepared material has an obvious internal porous structure with the existence of 5 at% Na ions. Besides, the obtained cathode material possesses excellent electrochemical characteristics. For example, it can deliver a high initial discharge capacity of 305.2 mA h g−1 between 2.0 V and 4.6 V at a rate of 0.1C at room temperature and the retention of the capacity is still as high as 88.2% after 200 cycles. Furthermore, the electrochemical impedance spectroscopy (EIS) results also show that the introduction of Na ions can decrease the charge transfer resistance of the as-prepared cathode material. The excellent electrochemical performance of the as-prepared cathode material can probably be attributed to the improved stability of the bulk lattice and the expanded Li slab space, which facilitates lithium ion diffusion and effectively enhances the stability of the layered structure of the materials.

Spinel/Layered Heterostructured Lithium-Rich Oxide Nanowires as Cathode Material for High-Energy Lithium-Ion Batteries

Lithium-rich oxide material has been considered as an attractive candidate for high-energy cathode for lithium-ion batteries (LIBs). However, the practical applications are still hindered due to its low initial reversible capacity, severe voltage decaying, and unsatisfactory rate capability. Among all, the voltage decaying is a serious barrier that results in a large decrease of energy density during long-term cycling. To overcome these issues, herein, an efficient strategy of fabricating lithium-rich oxide nanowires with spinel/layered heterostructure is proposed. Structural characterizations verify that the spinel/layered heterostructured nanowires are a self-assembly of a lot of nanoparticles, and the Li4Mn5O12 spinel phase is embedded inside the layered structure. When the material is used as cathode of LIBs, the spinel/layered heterostructured nanowires can display an extremely high invertible capacity of 290.1 mA h g-1 at 0.1 C and suppressive voltage fading. Moreover, it exhibits a favorable cycling stability with capacity retention of 94.4% after charging/discharging at 0.5 C for 200 cycles and it shows an extraordinary rate capability (183.9 mA h g-1, 10 C). The remarkable electrochemical properties can be connected with the spinel/layered heterostructure, which is in favor of Li+ transport kinetics and enhancing structural stability during the cyclic process.