WO3 modified LiNi0.8Co0.1Mn0.1O2 materials were got by a wet method. Structure parameters, micromorphology, element distribution of the modified and bare NCM materials were compared by different ...detection methods, such as XRD, SEM, EDS and TEM. The results reveal that there was no significant change in morphology before and after modification, and the distribution of tungsten was relatively uniform. In addition, tungsten oxide surface modification layer does exist by TEM, FFT and XPS analysis, and affects the distribution and valence states of surface elements. Furthermore, it is found that the micro amount of tungsten oxide modified NCM material is beneficial to the improvement of rate performance and cycle stability, especially at high cutoff voltage. Then the effect of modification on the electrochemical properties was conducted by CV, EIS and SEM detection after cycle. It is displayed that the particles after modification have no cracks, and the polarization and impedance decrease to varying degrees. This simple and feasible method has a good prospect for improving the cyclic stability of Ni-rich materials.
•Tungsten oxide modified LiNi0.8Co0.1Mn0.1O2 material were first put forward.•This simple and feasible method has a good prospect for improving the cyclic stability of Ni-rich materials.•The different amounts of tungsten oxide were compared, the addition of 0.25% has the best effect.
LiNi1−x−yCoxAlyO2 is a commonly used Ni-rich cathode material because of its relatively low cost, excellent rate capability and high gravimetric energy density. Surface modification is an efficient ...way to overcome the shortcomings of Ni-rich cathodes such as poor cycling stability and poor thermal stability. A high-powered concentration-gradient cathode material with an average composition of LiNi0.815Co0.15Al0.035O2 (LGNCAO) has been successfully synthesized by using spherical concentration-gradient Ni0.815Co0.15Al0.035(OH)2 (GNCA)as the starting material. An efficient design of the Al3+ precipitation method is developed, which enables obtaining spherical GNCA with ∼10 μm particle size and high tap density. In LGNCAO, the nickel and cobalt concentration decreases gradually whereas the aluminum concentration increases from the centre to the outer layer of each particle. Electrochemical performance and storage properties of LGNCAO have been investigated comparatively. The LGNCAO displays better electrochemical performance and improved storage stability than LNCAO.
•Al gradient doping is investigated to modify LiNiO2-based materials.•Al gradient doped cathode material is formed via a promoted precipitation method.•Al rich surface retards phase transformation and cation mixing.•LGNCAO displays better electrochemical performance and promoted storage property.
•LiMnPO4 was introduced to modify Ni-rich cathode materials.•LiMnPO4 uniformly coated NCA composite has been constructed successfully.•Olivine structured skin restrains the formation of residues on ...NCA during cycling.•LiMnPO4 improves the structural and thermal stability of NCA@LMP.
LiNi0.80Co0.15Al0.05O2 has been widely pursued as an alternative to LiCoO2 cathode materials for lithium ion batteries because of its high capacity and acceptable cycling property. However, that NCA can react with commercialized electrolyte during cycling restrains its wide use. Here, olivine structured LiMnPO4 has been introduced to modify the surface of NCA by a sol-gel method. Characterizations from structure, morphology and composition analysis technologies demonstrate that a LiMnPO4 layer has been uniformly coated on NCA particles. The electrochemical performance and thermo stability of modified samples are characterized by electrochemical tests, XRD and metallic nail penetration tests. The olivine structured skin, which provides structural and thermal stability, is used to encapsulate the high powered core via using the effective coating technique. The modified material displays a high discharge capacity of 211.0mAhg−1 at 0.2C and better rate performance and promoted cycling stability than the uncoated control sample. Furthermore, the thermal stability of coated sample in the delithiated state is upgraded to the pristine powders remarkably.
LiNi0.8Co0.15Al0.05O2 crystals with ∼4 μm particle size have been synthesized from spherical Ni0.8Co0.15Al0.05(OH)2 precursors via a two-step treatment strategy. A specific surface area controllable ...precipitation method was introduced to synthesize Ni1-x-yCoxAly(OH)2 hydroxides with large specific surface area. Spherical hydroxides with large specific area and excess LiOH calcination technique ensure the LiNi0.8Co0.15Al0.05O2 crystals with mono dispersed micrometer scaled particle distribution and perfect α-NaFeO2 layered structure. Water washing process wipes off the LiOH and Li2CO3 impurities from the cathodes efficiently without structural degradation. The LiNi0.8Co0.15Al0.05O2 prepared via 15% excess lithium calcination presents an improved compacting density of 3.8 g cm−3. The modified cathode material shows an initial discharge capacity of 174.5 mAh g−1 at 1C rate and 91.7% capacity retention after 100 cycles. The mono dispersed micron scaled morphology together with high structural stability endows the LNCAO material with superior compacting density and cycling capability for lithium ion batteries with high energy density.
•NCA precursors with large specific surface area have been synthesized.•Mono dispersed micron scaled LNCAO is prepared by an excessive lithium treatment.•Morphology modified samples endows a higher compacting density than commercial NCA.•Mono dispersed micron scaled Ni rich cathode shows promoted cycling capability.
Layered LiNi0.5Co0.2Mn0.3O2 (NCM523) material has been functionally coated with a uniform and thin layer of Li2SiO3 via a two-step method. Owing to its high lithium ion conduction and excellent ...structural stability against electrolyte decomposition, Li2SiO3 could greatly improve the Li+ ion diffusion rate and ameliorate the electrochemical capability of the layered oxide materials. Electrochemical tests illustrate that Li2SiO3 used as a Li+-ion conductor greatly improves electrochemical performance of the NCM523 cathode at high current density under high cutoff voltage. Particularly, the Li2SiO3-modified sample delivers an initial capacity of 140.0 mAh g−1 and remains 134.1 mAh g−1 even at a high current density of 10 C after 100 cycles, while the capacity of the pristine decreased sharply to 81.5 mAh g−1. The capacity retention of Li2SiO3-modified NCM523 is 96.1%, while only 55.3% for the bare sample. This result demonstrates an efficient method for the Li2SiO3-modified NCM523 cathode with enhanced electrochemical performance, which has a certain reference for other cathode materials of Li-ion batteries.
LiNi0.5Co0.2Mn0.3O2 has been functionally coated with Li2SiO3 via a two-step method. The Li2SiO3-coated sample shows improved electrochemical properties. Display omitted
•LiNi0.5Co0.2Mn0.3O2 has been functionally coated with Li2SiO3 via a two-step method.•Li2SiO3 possesses a high Li+-ion conduction and excellent structural stability.•The Li2SiO3-coated sample shows improved electrochemical properties.
LiNi0.8Co0.15Al0.05O2 cathode material for lithium-ion batteries is synthesized by sintering the precursor Ni0.8Co0.15Al0.05OOH, which is prepared from the corresponding metal sulphates solution by a ...co-oxidation-controlled crystallization method. The effects of calcination temperature and time on the electrochemical performance of the material are investigated on the basis of TG-DSC analysis. XRD analyses show that the powders obtained by calcination at 700 ?C for 6 h have the best-ordered hexagonal layer structure. SEM images show that these powders are spherical particles with diameter in the 5--12 Delta *mm range. The XPS measurement and the chemical titration display that Ni ions of these powders are in the form of Ni3+. The charge--discharge tests demonstrate that these powders have the best electrochemical properties, with an initial discharge capacity of 196.8 mAh g-1 and capacity retention of 96.1% after 50 cycles when cycled at a current density of 0.2 C between 2.8 and 4.3 V. Besides, these powders have also exhibited excellent rate capability and high-temperature performance.
The storage properties of LiNi0.8Co0.15Al0.05O2 and LiCoO2-coated LiNi0.8Co0.15Al0.05O2 have been investigated comparatively. It is found that the latter exhibits better storage stability than the ...former. After storage in air at different relative humidities, LiCoO2-coated LiNi0.8Co0.15Al0.05O2 shows little changes in the aspects of weight, nickel oxidation state, moisture and carbon contents and electrochemical performance. However, for LiNi0.8Co0.15Al0.05O2, the higher the air humidity is, the bigger these aspects change. Fourier transformed infrared (FTIR) spectrum reveals that LiCoO2-coated LiNi0.8Co0.15Al0.05O2 is resistant to H2O and CO2 in air. X-ray photoelectron spectroscopy gives evidence that the LiCoO2 coating layer suppresses effectively the reactions between LiNi0.8Co0.15Al0.05O2 and atmosphere, which contributes to the enhancement of storage performance of LiCoO2-coated LiNi0.8Co0.15Al0.05O2.
► LiCoO2-coated LiNi0.8Co0.15Al0.05O2 shows better storage stability compared to LiNi0.8Co0.15Al0.05O2. ► The properties of LiCoO2-coated LiNi0.8Co0.15Al0.05O2 have almost nothing to do with the air humidity. ► LiCoO2-coated LiNi0.8Co0.15Al0.05O2 is resistant to H2O and CO2 in air. ► The LiCoO2 coating layer suppresses effectively the reactions between LiNi0.8Co0.15Al0.05O2 and atmosphere.
Chromic oxide (Cr
2
O
3
) is one of the most important chromic salts and is widely used in industrial applications. Traditionally, Cr
2
O
3
is prepared from chromium trioxide (CrO
3
) or sodium ...dichromate (Na
2
Cr
2
O
7
), both of which are manufactured from chromite ore. However, traditional manufacturing processes are time-consuming, inefficient, and energy-consuming, and they can catheuse severe environmental pollution by discharging large quantities of solid residues containing Cr in the form of Cr(VI) compounds. These compounds are also harmful to human health. Therefore, developing an environmentally friendly production process is of great concern to the chromic oxide industry. In this study, a new method for producing Cr
2
O
3
without hexavalent chromium pollution was investigated. In this novel process, 97% of the total Cr—in the form of chromium sulfate (Cr
2
(SO
4
)
3
)—and Fe are leached from ferrochrome alloy using sulfuric acid. The concentration of Fe in the Cr
2
(SO
4
)
3
solution can be reduced to 2 mg/L after precipitating with oxalic acid and extracting with di (2-ethylhexyl) phosphate. Cr
2
O
3
is then produced by precipitating Cr from the Cr
2
(SO
4
)
3
solution with sodium hydroxide, followed by calcination of the precipitated Cr(OH)
3
at 500°C. Using this method, Cr
2
O
3
with a purity of up to 99.3% was obtained in this study. Throughout the process, Cr existed only in the form of Cr(III); thus, the pollution caused by hexavalent Cr was eliminated, and environmentally friendly production of Cr
2
O
3
was achieved.
•LiNi1/3Co1/3Mn1/3O2 was firstly used as a coating layer for LiNi0.8Co0.15Al0.05O2.•The coating layer is composed of small particle with the size of 10–50nm that grows into flocculent shape.•The ...thickness of the layer is about 300nm.•Samples displaying good rate capability and cyclic stability.
Electrochemically active material, LiNi1/3Co1/3Mn1/3O2, was chosen to coat LiNi0.8Co0.15Al0.05O2 particle by a co-precipitation method with a weight ratio of 3:97. The thickness of coating layer is about 300nm observed clearly by cross-section SEM photos. The coated material showed better electrochemical performance than that of the un-coated sample. At room temperature, the initial discharge capacity of the coated material was 188.2mAhg−1 at 0.2C between 2.8 and 4.3V and retained 96.2% after 100cycles. Moreover, the discharge capacities of the coated cathode material at 50°C could retain 163.2mAhg−1 after 100cycles. The composite also had a good rate performance with a capacity of about 146.3mAhg−1 at 2C rate. Electrochemical impedance spectroscopy measurements showed that the coated material had a lower charge-transfer resistance.
In the field of electrochemistry, Li
1.2
Ni
0.13
Co
0.13
Mn
0.54
O
2
(LRNCM) has become the research hotspot and of the cutting edge among lithium (Li)–rich cathode materials due to its favorable ...specific discharge capacity. However, the material involves various shortcomings, including structural transformation, poor cycling, and poor rate properties, which are hindering its commercialization. This work examined a wet-coating modification of the Li-rich manganese (Mn)–based cathode material using polyaniline (PANI), a material that exhibits superior electronic conductivity and is beneficial to the migration of electrons. A thin PANI-modified layer, functioning as a physical boundary, protects the cathode material from hydrofluoric acid corrosion and can effectively promote the transmission of electrons. It was found that the structural stability and the electrochemical property of the cathode were enhanced, with the LRNCM@PANI demonstrating an excellent cycling performance and an 82% capacity retention for 100 cycles (2.0–4.8 V, 0.2 C). The specific discharge capacity of the material coated with 1%PANI was around 36.9 mAh g
−1
higher than the uncoated electrode at 5 C. Overall, the results indicated that PANI coating is a remarkable means of enhancing the structural stability and electrochemical properties of Li-rich Mn-based cathode electrodes.
