Yuan Xue

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.

Controllable synthesis of hierarchical ball-in-ball hollow microspheres for a high performance layered Li-rich oxide cathode material

Layered Li-rich oxide (LLRO) is an attractive candidate for high-energy-density and high-voltage cathode material for next generation lithium ion batteries because of its high specific capacity and low cost. There still remain challenges in simultaneously achieving a multi-functional structure and composition in a LLRO, to achieve better electrochemical performance. Here we report a controllable co-precipitation and calcination method to synthesize LLRO by tuning the crystal nucleation, growth and heterogeneous contraction processes. The resultant LLRO adopts a hierarchical ball-in-ball hollow structure consisting of uniform multi-elemental (Mn–Ni–Co) primary nanocrystals, and exhibits high reversible capacity, remarkable cycle stability and superior rate performance. As a result, the resultant LLRO presents a high capacity of 193 mA h g−1 at 3C (a current density of 750 mA g−1) with a capacity retention of 87.6% after 400 cycles, and exhibits a capacity of 132 mA h g−1 at a high rate of 10C; moreover, it displays a quite slow voltage decay of ∼240 mV and a high energy density of 668 W h kg−1 after 200 cycles at 1C. The excellent electrochemical performance can be attributed to the combined merits of the multi-functional structure and composition, wherein the hierarchical hollow architecture facilitates efficient electron/ion transport and high structural stability, while multi-elemental components offer high reversible capacity.

Electrochemical properties of high-voltage LiNi0.5Mn1.5O4 synthesized by a solid-state method

LiNi0.5Mn1.5O4 cathode material has been synthesized by a solid-state reaction designedly using industrial raw materials (Li2CO3, NiO and electrolytic MnO2) in bulk scale, which are all used without further purification. The aim is to find the optimal preparation process of LiNi0.5Mn1.5O4 material for commercial application. The synthesis temperatures are adjusted to form a disordered Fdm structure at 800–950 °C for 12 h and then at 600 °C for 6 h. Meanwhile, some powders have also been calcined at 850 °C for 8–14 h and next annealed at 600 °C for 6 h. XRD patterns, SEM micrographs and distribution curves of particle size shows that the LiNi0.5Mn1.5O4 cathode material calcined at 850 °C for 12 h and then annealed at 600 °C for 6 h exhibits the best crystallinity, crystal shape as well as the best normal distribution. Electrochemical tests show that the LiNi0.5Mn1.5O4 material synthesized at 850 °C for 12 h and then annealed at 600 °C for 6 h has the highest capacity and excellent rate capability. After 200 cycles, the capacity retentions of the sample at 1, 2 and 5 C are as high as 97.8%, 98.5% and 98.0% of its initial capacities (120.8, 118.1 and 111.2 mA h g−1), respectively. The fundamental findings in this work can be applied to guide the synthesis of spinel LiNi0.5Mn1.5O4 as high performance electrode materials for lithium ion batteries, especially for industry.

Layered-spinel capped nanotube assembled 3D Li-rich hierarchitectures for high performance Li-ion battery cathodes

While Li-rich Mn-based layered oxide is an appealing candidate for high energy density and high-voltage cathode materials for Li-ion batteries (LIBs), its applications are severely restricted by its low coulombic efficiency and poor rate capability. Herein, we report an effective approach to fabricate layered-spinel capped nanotube assembled 3D Li-rich hierarchitectures, by using a hydrothermal and ionic interfusion method. The unique 3D hollow hierarchical structure of the resulting material greatly shortens the pathways of electron and ion transfer, while maintaining reliable structural stability. Moreover, layered-spinel multicomponents introduce more effective 3D Li-ion diffusion channels (an excellent Li-ion diffusion coefficient of 1.55 × 10−10 cm2 s−1) and offer high coulombic efficiency. The structure–composition–property relationship is investigated by hierarchical structure controllable synthesis, Rietveld refinement crystallographic analysis and Li-ion transport kinetics measurement. As a result, when utilised as a cathode material for LIBs, this 3D Li-rich hierarchitecture delivers a high capacity of 293 (±3) mA h g−1 at 0.1C, shows a superior capacity retention of 89.5% after 200 cycles at 1C and exhibits a high capacity of 202 (±3) mA h g−1 even at 5C.

Improved electrochemical performance of LiNi0.4Ti0.1Mn1.5O4 as cathode of lithium ion battery by carbon-coating

The effects of Ti substitution for Ni, carbon coating on the structure and electrochemical properties of LiMn1.5Ni0.5O4 are studied. LiMn1.5Ni0.5O4, LiNi0.4Ti0.1Mn1.5O4 and carbon-coated LiNi0.4Ti0.1Mn1.5O4 cathode materials have been synthesized by a solid-state reaction using industrial raw materials in bulk scale. X-ray diffraction clearly shows that LiMn1.5Ni0.5O4 has higher crystallinity after Ti doping. Scanning electron microscopy clearly exhibits that Ti doping does not change the basic spinel structure, as well as coated carbon layer covers the surfaces of the LiNi0.4Ti0.1Mn1.5O4 particles. In addition, charge–discharge tests indicate that LiNi0.4Ti0.1Mn1.5O4 sample has higher discharge capacities at the rates of 0.5, 1 and 3 C at 25 °C. It should be noted that carbon-coated LiNi0.4Ti0.1Mn1.5O4 shows higher discharge capacities at the rates of 5, 7 and 10 C at 25 °C as well as various rates for 55 °C. Cyclic performances developed at 25 and 55 °C demonstrate that the capacity retention is remarkably improved compared to the two uncoated samples. The influence of the Ti-doping and carbon-coating on the coulombic efficiency at high temperature (55 °C) has also been investigated. Among the various samples investigated, surface modification with carbon gives an improved coulombic efficiency. The remarkably enhanced electrochemical properties of the carbon-coated sample may be because of the suppression of the solid electrolyte interfacial (SEI) layer development and faster kinetics of both the Li+ diffusion, as well as the charge transfer reaction.

Synthesis and performance of hollow LiNi0.5Mn1.5O4 with different particle sizes for lithium-ion batteries

High voltage spinel LiNi0.5Mn1.5O4 is a promising cathode material for next generation lithium ion batteries. A simple method of synthesizing hollow LiNi0.5Mn1.5O4 spinel using MnCO3 as the manganese resource is presented. The hollow structure forms during the calcination process at 850 °C. The transformation from MnCO3 to manganese oxide and inter-diffusion of Mn and Ni atoms are excluded as reasons for the formation of the hollow structure. Four hollow LiNi0.5Mn1.5O4 samples with different particle sizes were synthesized by controlling the reactant concentration. The effects of particle size on the electrochemical performance of hollow LiNi0.5Mn1.5O4 have been investigated in detail. The hollow LiNi0.5Mn1.5O4 samples with particle size less than 1 μm and some small broken particles of about 200 nm show poor rate capability and cycling performance due to their poor contact with conductive additive and high interface resistance. The hollow LiNi0.5Mn1.5O4 samples with diameters of 2 or 6 μm exhibit better rate capability and cycling performance. This is because most of the micro-sized particles can make direct contact with the conductive additive and have low interface resistance; moreover, the hollow structure also decreases the Li+ ion and electron diffusion distance.

Facile strategy of NCA cation mixing regulation and its effect on electrochemical performance

The cation mixing of LiNi0.8Co0.15Al0.05O2 materials was regulated by a facile strategy via control of oxygen flow rate during sintering. The cation mixing first decrease and then increased with the increasing oxygen flow rates. The effects of cation mixing on the electrochemical performance of LiNi0.8Co0.15Al0.05O2 materials were studied in detail. Their initial discharge capacities, rate capabilities and cycling retentions (both at room temperature and 55 °C) increase with decreasing cation mixing, and then decrease with increasing cation mixing, while their Rct (charge transfer resistance) and oxidation/reduction peaks of the CV curves reveal the opposite trend. LiNi0.8Co0.15Al0.05O2, which possesses the smallest cation mixing, had an initial discharge capacity of 191.3 mA h g−1 with 86.4% coulombic efficiency at 0.1C rate between 2.8 V and 4.3 V (vs. Li/Li+), which was maintained at 144.1 mA h g−1 and 139.1 mA h g−1 after 300 cycles at 1C rate at 25 °C and 55 °C, respectively. It is clear that the NCA sample with smaller cation mixing presents better electrochemical performance.

A simple method for industrialization to enhance the tap density of LiNi0.5Co0.2Mn0.3O2 cathode material for high-specific volumetric energy lithium-ion batteries

Electrode materials with high tap densities and high specific volumetric energies are the key to large-scale industrial applications for the lithium ion battery industry, which faces huge challenges. LiNi0.5Co0.2Mn0.3O2 cathode materials with different particle sizes are used as the raw materials to study the effect of the mass ratio of mixed materials on the tap density and electrochemical performance of mixed materials in this work. Physical and electrochemical characterizations demonstrate that the tap density of mixed powders with different particle sizes is higher than those of materials with a single particle size. The tap density of as-prepared material has a decreasing trend with the increase of the ratio of 9 μm sized particle in the materials. The highest tap density among all of the kinds of materials reaches up to 2.66 g cm−3. Besides, the mixed material with a mass ratio of 7 : 2 : 1 has a bigger specific surface area and it presents better cycle behaviors and rate capability than other materials. The specific volumetric capacity of this mixed sample reaches up to 394.3 mA h cm−3 with 1C rate charge/discharge, and it has improvements of 8.5%, 22.2% and 40.6% over any single particle size of 9 μm, 6 μm and 3 μm, respectively, which contributes to the industrial production of Li–Ni–Co–Mn–O cathode materials for lithium ion batteries.