Lithium-rich Cathode Material Li1 Research Articles

Cadmium Modification of the Lithium-Rich Cathode Material Li1.2Ni0.133Mn0.534Co0.133O2

Cadmium Modification of the Lithium-Rich Cathode Material Li1.2Ni0.133Mn0.534Co0.133O2

Sol-gel synthesis of nano Li1.2Mn0·54Ni0·13Co0·13O2 cathode materials using DL-lactic acid as chelating agent

Lithium-rich cathode materials Li1·2Mn0·54Ni0·13Co0·13O2 (LMNCO) are prepared by sol-gel method using dl-lactic acid as chelating agent. The effect of pH on crystal structures, morphologies, particle sizes, and electrochemical properties of cathode materials are studied by X-ray diffractometry (XRD), scanning electron microscopy (SEM), nanoparticle analysis, charge–discharge tests, and electrochemical analysis. The Li1·2Mn0·54Ni0·13Co0·13O2 cathodes exhibit well-ordered layered structures consisting of hexagonal LiMO2 and monoclinic Li2MnO3 with smooth surfaces and well-crystallized particles (100–500 nm). LMNCO-7.0 exhibits smaller particle sizes than LMNCO-5.5 and LMNCO-8.5 and better electrochemical performance. The first discharge capacity and Coulombic efficiency of LMNCO-7.0 are 232.31 mAh g−1 and 73.2%, respectively. After 50 cycles, discharge capacity of LMNCO-7.0 decrease to 194.93 mAh g−1. LMNCO-7.0 cathode shows superior discharge capacity and rate performance due to its low charge transfer impedance and small average quasi-spherical particle diameter.

Enhanced rate capability and cycling stability of lithium-rich cathode material Li1.2Ni0.2Mn0.6O2 via H3PO4 pretreating and accompanying Li3PO4 coating

H3PO4 pretreated and Li3PO4 coated Li-rich materials Li1.2Ni0.2Mn0.6O2 have been prepared via hydrothermal followed by a facile modified method. The pretreated process partially extracts Li and O from lattice, results in pre-activation of Li2MnO3 component and the formation of spinel phase. A stable Li3PO4 coating is formed on the surface of the material during the subsequent heat treatment. H3PO4 pretreatment and Li3PO4 coating are skillfully combined using a simple method. Electrochemical studies exhibit that the electrochemical performance of Li1.2Ni0.2Mn0.6O2 is obviously improved after surface modification. The surface treated material with 0.04 mol L−1 H3PO4 shows more excellent electrochemical properties than those of Li1.2Ni0.2Mn0.6O2 cathode, with a high specific discharge capacity of 262.6 mAh g−1 at 0.1 C, a great capacity retention of 92.2% at 1 C after 100 cycles, and an outstanding rate capability reaching 105.4 mAh g−1 at 10 C. The enhanced performance is caused by the formation of spinel phase and Li3PO4 coating layer, which can accelerate the migration of Li+ and facilitate the charge transfer reaction. The Li3PO4 coating also inhibits the dissolution of transition metal ions and enhances the stability of electrode/electrolyte interface.

Surface-Functionalized Coating for Lithium-Rich Cathode Material To Achieve Ultra-High Rate and Excellent Cycle Performance.

Although the lithium-rich cathode material Li1.2Mn0.54Ni0.13Co0.13O2, as a promising cathode material, has a high specific capacity, it suffers from capacity decay and discharge voltage decay during cycling. In this work, the specific capacity and discharge voltage of Li1.2Mn0.54Ni0.13Co0.13O2 are stabilized by surface-functionalized LiCeO2 coating. We have conducted LiCeO2 coating via a mild synchronous lithium strategy to protect the electrode surface from electrolyte attack. This optimized LiCeO2 coating has high Li+ conductivity and abundant oxygen vacancies. The results demonstrate that 3% LiCeO2-coated Li1.2Mn0.54Ni0.13Co0.13O2 exhibits the highest capacity retention rate at 1, 2, and 5 C after 200 cycles, which were 84.3%, 85.4%, and 86.3%, respectively. The discharge specific capacity was almost 1.3, 1.4, and 1.4 times that of the pristine electrode. In addition, the 3% LiCeO2 electrode exhibited the least voltage decay of 0.409, 0.497, and 0.494 V at 1, 2, and 5 C, which was only about half of the pristine electrode. It should not be overlooked that the 3% LiCeO2 electrode still exhibits a high capacity at high current densities of 1250 mA g-1 (5 C) and 2500 mA g-1 (10 C), and its specific discharge capacities are 190.5 and 160.6 mAh g-1, respectively. These outstanding electrochemical properties benefit from surface-functionalized LiCeO2 coatings. To better understand the mechanism of oxygen loss of lithium-rich materials, we propose the lattice oxygen migration path of the LiCeO2-coated electrodes during the cycle. Our research provides a possible solution to the poor rate capability and cycle performance of cathode materials through surface-functionalized coatings.

Improving electrochemical performance of lithium-rich cathode material Li1.2Mn0.52Ni0.13Co0.13W0.02O2 coated with Li2WO4 for lithium ion batteries

Lithium-rich manganese-based cathode materials face severe challenges, like initial irreversible capacity loss, poor cycling performance and rate capability, which seriously restrict their application in broader fields. In this work, Li2WO4-coated Li [Li0.2Mn0.52Ni0.13Co0.13W0.02]O2 has been successfully prepared by the sol-gel method with a calcination process. The measurements, such as X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and transmission electron microscopy, are used to demonstrate Li2WO4 dispersion on the material surface. After coating with appropriate contents of Li2WO4, the materials display superior cycling performance and rate capability as well as low voltage decay. The optimal amounts of coating correspond to high capacity retentions of 87.5% at 1C and 88.7% at 5C, while the values only reach 72.9% and 75.9% for the pristine sample, respectively. In particular, when the coating content reaches 3 wt%, the rate capability is remarkably improved. The Li2WO4 coating layer can alleviate the corrosion of active materials and side reactions with electrolyte to enhance the cathode structural stability.

Influence of the pH of li-rich Li1.2Mn0.54Ni0.13Co0.13O2 on the electrochemical performance by sol–gel method

The positive electrode material of the lithium-rich layered oxide has poor capability, and its cycle stability and rate characterizations have not been satisfactory. The lithium-rich cathode material Li1.2Mn0.54Ni0.13Co0.13O2 with different particle sizes was obtained by adjusting the pH by sol–gel method. The results show that the electrochemical performance of the material is optimal at pH = 9.0. It initial discharge capacity of 262.5 mAh/g at 0.1 C between 2.0 and 4.8 V. The high reversible discharge capacities is still of 161.0 and 133.7 mAh/g after 100 cycles at 0.5 C and 2 C, with a high capacity retention of 80.46% and 84.14%, respectively. This excellent electrochemical performance is attributed to smaller and uniform particles

Improving the electrochemical performance of lithium-rich cathode materials Li1.2Mn0.54Ni0.13Co0.13O2 by a method of tungsten doping

In order to alleviate the capacity and voltage attenuation of the Li-rich materials, a series of tungsten-doped Li1.2Mn0.54-xNi0.13Co0.13WxO2 (0 ≤ x ≤ 0.04) were produced through a sol-gel method. The XRD patterns exhibit a representative structure of hexagonal α-NaFeO2 and a well-layered structure. XPS index that the valence of W is 6+. From the results of charge-discharge cycling, appropriate W doping for Li-rich layered oxides can prominently raise its performance. After 100 cycles, the 0.02W-doped sample obtain a capacity retention ratio of 82.6% (154.7 mAh g−1) at 1 C, but the ratio for the pure sample only is 77.5% (121.7 mAh g−1) at the same conditions. Meanwhile, the 0.02W-doped sample can obtain the best properties at different rates. The results reveal that the modification method of W-doping can stabilize the structure of the Li-rich materials and enhance the properties.

The Effects of Trace Yb Doping on the Electrochemical Performance of Li-Rich Layered Oxides.

Layered lithium-rich cathode materials are one of the most promising cathode materials owing to their higher mass energy density than the commercial counterparts. A series of trace Yb-doped lithium-rich cathode materials Li1.2 Mn0.54 Ni0.13 Co0.13-x Ybx O2 (0≤x≤0.050) were synthesized and the effects were investigated by XRD, X-ray photoelectron spectroscopy, and high-resolution TEM. The participation of Yb ions in electrochemical reactions and the larger binding energy of Yb-O than M-O (M=Mn, Ni, Co), which expands the lithium layer spacing and stabilizes the oxygen stacking, resulted in excellent performance of materials doped with a limited Yb content (x≤0.005). However, higher doping amounts (x>0.005) significantly increased the charge-transfer impedance and led to a sharp deterioration in electrochemical performance. The reason lies in the large difference in ionic radius between the transition metals (Mn, Co, and Ni) and Yb. There is an upper limit to the amount of Yb ions in the lattice. If the amount of Yb is higher than the limit, excess Yb ions enter the Li layers instead of staying in the transition-metal layers or even segregate on the surface and form electrochemically inert oxides.

MnO2 nanowires as precursor synthesis of lithium-rich cathode material with enhanced electrochemical performances

Lithium-rich cathode material Li1.2Mn0.54Ni0.13Co0.13O2 for lithium-ion battery has been successfully synthesized through combination of co-precipitation and α-MnO2 nanowires as precursor. The X-ray diffraction (XRD) results reveal that the as-obtained material can exhibit well-layered structure and crystallization. The as-prepared sample has been investigated by the scanning electron microscope (SEM) and transmission electron microscopy (TEM). The possible reason for the formation of polyhedron has been presented. The results of electrochemical performance reveal that the as-prepared sample with combination of two methods can provide an initial discharge specific capacity of 247.5 mAh g−1 at 0.2 C within a potential range of 2.0–4.8 V, and this material can also deliver a discharge specific capacity of 181.8 mAh g−1 at 2 C with 97.8% capacity retention after 100 cycles. Hence, it is proposed that combination of two methods might be a promising strategy to prepare electrode cathode materials with improved performance.

Sheet-like Li1.2Mn0.54Ni0.16Co0.10O2 prepared by glucose-urea bubbling and post-annealing process as high capacity cathode of Li-ion batteries

Sheet-like lithium-rich cathode materials Li1.2Mn0.54Ni0.16Co0.10O2 (LMNCO) assembled by primary grains of 100–500 nm in sizes were facilely prepared by a glucose-urea bubbling and post-annealing process. The post-annealing temperature was found to play an important role on the grain size, crystallinity, cation ordering and electrochemical performance of the cathode materials. The sample post-annealed at 900 °C showed larger grains, higher crystallinity, better layered structure, higher lithium storage capacity and better rate performance than the one annealed at 800 °C. An initial discharge capacity of above 300 mA h g−1 was obtained at 0.1 C (20 mA g−1) for the sample annealed at 900 °C, and at 1, 2, 5 and 10 C, discharge papacies of 223, 192, 157 and 128 mA h g−1 were achieved respectively. The material synthesizing process proposed in this study may be extended to prepare a wide range of sheet-like functional oxides that may be potentially applied in energy storage or other fields.

Li-rich nanoplates of Li1.2Ni0.13Co0.13Mn0.54O2 layered oxide with exposed {010} planes as a high-performance cathode for lithium-ion batteries

The layered lithium-rich cathode material Li1.2Ni0.13Co0.13Mn0.54O2 crystallizes with an α-NaFeO2 structure, through which Li+ ions are transported along two-dimensional channels. In this work, nanoplates of Li1.2Ni0.13Co0.13Mn0.54O2 (NP-LNCMO) with exposed {010} planes are successfully synthesized. The formation of open structures provides unimpeded paths for Li+ ion intercalation/deintercalation. The synthesis involves the use of ethylene glycol with two hydroxyl groups as the solvent, which can also react with the transition metal ions to yield plate-like structures with exposed {010} planes. NP-LNCMO displays a high specific discharge capacity of 288.9 mAh g−1 at 0.1 C (1 C = 300 mA g−1) and an excellent rate capability (a discharge capacity of 109.7 mAh g−1 at 15 C). Furthermore, negligible voltage decay occurs during 50 charge/discharge cycles. The excellent electrochemical performance of NP-LNCMO can be attributed to the formation of nanoplates with exposed electrochemically active {010} planes.

Enhancing coulombic efficiency and rate capability of high capacity lithium excess layered oxide cathode material by electrocatalysis of nanogold

A lithium-rich cathode material Li1.2Mn0.56Ni0.16Co0.08O2 modified with nanogold (Au@LMNCO) for lithium-ion (Li-ion) batteries was prepared using co-precipitation, solid-state reaction and surface treatment techniques.

Structural and electrochemical characterization of Mg-doped Li1.2[Mn0.54Ni0.13Co0.13]O2 cathode material for lithium ion batteries

Magnesium doped lithium-rich cathode material Li1.2[Mn0.54Ni0.13Co0.13]1−xMgxO2 (x=0, 0.005, 0.007, 0.01 and 0.012) is prepared via coprecipitation method, followed by Mg doping through dry/wet grinding and solid reaction sintering method. Among the synthesized Mg-doped materials, when x=0.01, this material demonstrates remarkably improved cycling performance with capacity retention ratio of 83% compared to 54% of pristine one after 100cycles at 1C rate. X-ray diffraction test of all samples shows that these materials are in the R3¯m (no. 166) space group and have a slight increase of the inter-slab distance with magnesium doping, which could reduce the barrier during the intercalation–deintercalation process of Li+ and stabilizes the crystal structure. The improvement in Li+ diffusion and crystal structure stability is also confirmed from the electrochemical impedance spectroscopy (EIS) analysis and cyclic voltammetry (CV) test.

Surface Modification of Li1.2Ni0.13Mn0.54Co0.13O2 by Hydrazine Vapor as Cathode Material for Lithium-Ion Batteries.

An artificial interface is successfully prepared on the surface of the layered lithium-rich cathode material Li1.2Ni0.13Mn0.54Co0.12O2 via treating it with hydrazine vapor, followed by an annealing process. The inductively coupled plasma-atomic emission spectrometry (ICP) results indicate that lithium ions are leached out from the surface of Li1.2Ni0.13Mn0.54Co0.12O2 by the hydrazine vapor. A lithium-deficiency-driven transformation from layered to spinel at the particle surface happens in the annealing process, which is proved by the results of X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM). It is also found that the content of the spinel phase increases at higher annealing temperature, and an internal structural evolution from Li1-xM2O4-type spinel to M3O4-type spinel takes place simultaneously. Compared to the pristine Li1.2Ni0.13Mn0.54Co0.12O2, the surface-modified sample annealed at 300 °C delivers a larger initial discharge capacity of 295.6 mA h g(-1) with a Coulombic efficiency of 89.5% and a better rate performance (191.7 mA h g(-1) at 400 mA g(-1)).

Eliminating voltage decay of lithium-rich li1.14 mn0.54 ni0.14 co0.14 o2 cathodes by controlling the electrochemical process.

A lithium-rich cathode material Li1.14 Mn0.54 Ni0.14 Co0.14 O2 (LNMCO) is prepared by a co-precipitation method. The issue of voltage decay in long-term cycling is largely eliminated by control of the charge-discharge voltage range. The LNMCO material exhibits 9.8 % decay in discharge voltage over 200 cycles between 2.0-4.6 V, during which the working voltage decays significantly, from 3.57 V to 3.22 V. The decay was decelerated by a factor of six by using a voltage window of 2.0-4.4 V, from 3.53 V to 3.47 V. IR and Raman spectra reveal that the transformation of layered structure to spinel is significantly retarded under 2.0-4.4 V cycling conditions. Transmission electron microscopy (TEM) was also applied for examining phase change in an individual particle during cycling, showing that the spinel phase occurs both at 2.0-4.6 V and at 2.0-4.4 V, but is not dominant in the latter. Normalization of Li can remove the additional impact on the voltage decay which is brought by different amounts of Li intercalation. The mechanism of no voltage decay at 2.0-4.4 V cycling is raised and electrochemical impedance spectrum data also support the hypothesis.

Effective enhancement of the electrochemical performance of layered cathode Li1.5Mn0.75Ni0.25O2.5via a novel facile molten salt method

A series of nanocrystalline lithium-rich cathode materials Li1.5Mn0.75Ni0.25O2.5 have been prepared by a novel synthetic process, which combines the co-precipitation method and a modified molten salt method.

Electrochemistry Characteristics of SmF3-Coated Lithium-Rich Cathode Material Li1.2Ni0.2Co0.08Mn0.52O2

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Modulating the Li+/Ni2+ replacement and electrochemical performance optimizing of layered lithium-rich Li1.2Ni0.2Mn0.6O2 by minor Co dopant

The influences of the Li+/Ni2+ replacement modulated by minor Co dopant on cyclic capacity and rate performance of lithium-rich cathode material Li1.2Ni0.2−z/2Mn0.6−z/2CozO2 (z = 0, 0.02, 0.04, 0.10) were investigated from the microstructural point of view by comprehensive techniques of HRTEM, EELS, SAED, and XRD.

Hierarchically porous micro-rod lithium-rich cathode material Li1.2Ni0.13Mn0.54Co0.13O2 for high performance lithium-ion batteries

Lithium-rich cathode material Li1.2Ni0.13Mn0.54Co0.13O2 with hierarchically porous micro-rod structures has been synthesized using a facile hydrothermal method. The morphology and XRD patterns explain the formation mechanism of the sample. Micro-rod oxalates precursor with rough surface is formed during the hydrothermal reaction, and then the product with hierarchically porous structures constructed of nanoparticles is synthesized during the sintering process at high temperatures. The electrochemical performance results show that the as-prepared sample exhibits high capacities, good cycleability and outstanding rate capability. It delivers discharge capacities of 280.7, 254.8, 232.3, 225.6, 201.7 and 172.7 mAh g−1 at 0.1C, 0.2C, 0.5C, 1C, 2C and 5C rates, respectively. The cycle voltammograms indicate the good reversibility of the as-prepared Li1.2Ni0.13Mn0.54Co0.13O2 material. The high onset temperature of the exothermal peak in the differential scanning calorimetry curve implies its good thermal stability. The good performance of the as-prepared material is endowed by its hierarchically porous structures.

Preparation and characterization of Li1.2Ni0.13Co0.13Mn0.54O2 cathode materials for lithium-ion battery

Lithium-rich cathode materials Li1.2Ni0.13Co0.13Mn0.54O2 with (sample SF) and without (sample SP) formamide was synthesized by a spray-dry method. The crystalline structure and particle morphology of as-prepared materials were characterized by X-ray diffraction and scanning electron microscope. The specific surface area (SSA) of the Li1.2Ni0.13Co0.13Mn0.54O2 prepared from different routes was determined by a five-point Brunauer–Emmett–Teller (BET) method using N2 as absorbate gas. Being compared with the material synthesized without spray-drying process (sample CP), sample SP has much higher SSA. The additive formamide is helpful to form regular and solid precursor particles in spray-drying process, which results in a slightly aggregation of grains and reduction of SSA for sample SF. The electrochemical activities of the materials are closely related to their morphology and SSA. In the voltage range of 2–4.8 V at 25 °C, sample SP present a discharge capacity of 257 mAh g−1 at 0.1 C rate and 170 mAh g−1 at 1 C rate. The sample CP delivered only 136 mAh g−1 when discharged at 1 C rate. The elevated specific capacity and rate capability are attributed to smaller primary particle and higher SSA. Both cycle performance and rate capability of Li1.2Ni0.13Co0.13Mn0.54O2 were improved when formamide was used in spray-dry process. Discharge capacity of SF is 140.5 mAh g−1 at 2 C rate, and that of SP is 132.3 mAh g−1. Overlarge SSA of SP may provoke serious side reaction, so that its electrochemical performance was deteriorated.