Ultrathin CeO2 coating for improved cycling and rate performance of Ni-rich layered LiNi0.7Co0.2Mn0.1O2 cathode materials

In this study, we have successfully coated the CeO₂ nanoparticles (CeONPs) layer onto the surface of the Ni-rich layered LiNi_0.7Co_0.2Mn_0.1O₂ cathode materials by a wet chemical method, which can effectively improve the structural stability of electrode. The X-ray powder diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS) are used to determine the structure, morphology, elemental composition and electronic state of pristine and surface modified LiNi_0.7Co_0.2Mn_0.1O₂. The electrochemical testing indicates that the 0.3?mol% CeO₂-coated LiNi_0.7Co_0.2Mn_0.1O₂ demonstrates excellent cycling capability and rate performance, the discharge specific capacity is 161.7?mA?h?g^?1 with the capacity retention of 86.42% after 100 cycles at a current rate of 0.5?C, compared to 135.7?mA?h?g^?1 and 70.64% for bare LiNi_0.7Co_0.2Mn_0.1O₂, respectively. Even at 5?C, the discharge specific capacity is still up to 137.1?mA?h?g^?1 with the capacity retention of 69.0%, while the NCM only delivers 95.5?mA?h?g^?1 with the capacity retention of 46.6%. The outstanding electrochemical performance is assigned to the excellent oxidation capacity of CeO₂ which can oxidize Ni²⁺ to Ni³⁺ and Mn³⁺ to Mn⁴⁺ with the result that suppress the occurrence of Li⁺/Ni²⁺ mixing and phase transmission. Furthermore, CeO₂ coating layer can protect the structure to avoid the occurrence of side reaction. The CeO₂-coated composite with enhanced structural stability, cycling capability and rate performance is a promising cathode material candidate for lithium-ion battery.     

LiNi0.1Mn0.1Co0.8O2 electrode material: Structural changes upon lithium electrochemical extraction

We reported here on the synthesis, the crystal structure and the study of the structural changes during the electrochemical cycling of layered LiNi_0.1Mn_0.1Co_0.8O₂ positive electrode material. Rietveld refinement analysis shows that this material exhibits almost an ideal α-NaFeO₂ structure with practically no lithium-nickel disorder. The SQUID measurements confirm this structural result and evidenced that this material consists of Ni²⁺, Mn⁴⁺ and Co³⁺ ions.Unlike LiNiO₂ and LiCoO₂ conventional electrode materials, there was no structural modification upon lithium removal in the whole 0.42 ≤ x ≤1.0 studied composition range. The peaks revealed in the incremental capacity curve were attributed to the successive oxidation of Ni²⁺ and Co³⁺ while Mn⁴⁺ remains electrochemically inactive.     

On the LiCo2/3Ni1/6Mn1/6O2 positive electrode material

LiCo_2/3Ni_1/6Mn_1/6O₂ layered oxide was synthesized by the combustion method that led to a crystalline phase with good homogeneity and low particles size. The structural properties of the prepared positive electrode material were investigated by performing XRD Rietveld refinement. Practically no Li/Ni mixing was detected evidencing that the studied compound adopts almost an ideal α-NaFeO₂ type structure. The Li||LiCo_2/3Ni_1/6Mn_1/6O₂ cell showed a discharge capacity of 199 mAh g⁻¹ when cycled in the 2.7–4.6 V potential range while the best cycling performances were recorded when the upper cut off is fixed at 4.5 V. Structural changes in Li_xCo_2/3Ni_1/6Mn_1/6O₂ with lithium electrochemical de-intercalation were studied using X-ray diffraction. This study clearly shows the existence of a solid solution domain in the 0.1 < x < 1.0 composition range while for x = 0.1, a new phase appears explaining the decrease of the electrochemical performance when the cell is cycled at high upper cut off voltage.     

Hydrothermal synthesis of layered Li[Ni1/3Co1/3Mn1/3]O2 as positive electrode material for lithium secondary battery

In attempts to prepare layered Li[Ni_1/3Co_1/3Mn_1/3]O₂, hydrothermal method was employed. The hydrothermal precursor, [Ni_1/3Co_1/3Mn_1/3](OH)₂, was synthesized via a coprecipitation route. The sphere-shaped powder precursor was hydrothermally reacted with LiOH aqueous solution at 170 °C for 4 days in autoclave. From X-ray diffraction and scanning electron microscopic studies, it was found that the as-hydrothermally prepared powders were crystallized to layered α-NaFeO₂ structure and the particles had spherical shape. The as-prepared Li[Ni_1/3Co_1/3Mn_1/3]O₂ delivered an initial discharge of about 110 mA h g⁻¹ due to lower crystallinity. Heat treatment of the hydrothermal product at 800 °C was significantly effective to improve the structural integrity, which consequently affected the increase in the discharge capacity to 157 (4.3 V cut-off) and 182 mA h g⁻¹ (4.6 V cut-off) at 25 °C with good reversibility.     

Facile strategy to fabricate Na2Li2Ti6O14@Li0.33La0.56TiO3 composites as promising anode materials for lithium-ion battery

A robust strategy has been developed to fabricate Na₂Li₂Ti₆O₁₄@Li_0.33La_0.56TiO₃ composites as promising anode materials for lithium-ion battery. Li_0.33La_0.56TiO₃ modification does not change the basic structure of Na₂Li₂Ti₆O₁₄ but enhances the lattice parameter because few trivalent lanthanum ions enter the crystal lattice of Na₂Li₂Ti₆O₁₄. All samples show similar morphology with a narrow size distribution ranged from 100 to 500?nm. HRTEM test demonstrates that a good conductive connection between the Na₂Li₂Ti₆O₁₄ and Li_0.33La_0.56TiO₃ layer is successfully formed. The electrochemical tests show that Na₂Li₂Ti₆O₁₄@Li_0.33La_0.56TiO₃ (5?wt%) sample exhibits the lowest charge-transfer resistance, highest reversibility of lithium insertion/extraction, and the largest Li-ion diffusion coefficient among all samples, and then shows the best electrochemical activity. Hence, the Na₂Li₂Ti₆O₁₄@Li_0.33La_0.56TiO₃ (5?wt%) electrode reveals the largest lithiation and delithiation capacities at each current density. The Na₂Li₂Ti₆O₁₄@Li_0.33La_0.56TiO₃ (5?wt%) shows excellent cycling stability with a delithiation capacity of 166.8?mAh?g^?1 at 500?mA?g^?1 after 100 cycles. However, the corresponding delithiation capacity of pristine Na₂Li₂Ti₆O₁₄ is only 136.9?mAh?g^?1 after 100 cycles. Li_.33La_.56TiO₃ modification is a direct and powerful design method to enhance the delithiation and lithiation capacities and cycling stability of Na₂Li₂Ti₆O₁₄.     

Fabrication and characterization of monodispersed Mn0.8Ni0.2Co2O4 mesoporous microspheres for supercapacitor application

The monodispersed Ni doped MnCo₂O₄ mesoporous microspheres were synthesized through a simple ammonium bicarbonate-assisted solvothermal route. The spinel-type crystal structure with a lattice parameter of 8.199?Å for Mn_0.8Ni_0.2Co₂O₄ composition was obtained by using X-ray diffraction analysis. The Brunauer?Emmett?Teller (BET) specific surface area of the sample was found to be 75.78?m² g^?1 with an average pore diameter of 9.88?nm. Electron microscopy studies revealed that the stable mesoporous microspheres are constituted by well-connected aggregates of nanoparticles. The influence of Ni doping on the pseudo-capacitance of MnCo₂O₄ electrode was investigated by means of cyclic voltammetry in 6?M KOH electrolyte. We found that the spinel-type Mn_0.8Ni_0.2Co₂O₄ mesoporous microspheres exhibit specific capacitances of 1822 F g^?1 at a scan rate of 5?mV/s. Furthermore, the electrochemical impedance spectroscopy analysis revealed the low resistance and good electrochemical stability of the sample.     

Magnesium ferrite nanoparticles as a magnetic sorbent for the removal of Mn2+, Co2+, Ni2+ and Cu2+ from aqueous solution

The aim of this research was to prepare magnesium ferrite (MgFe₂O₄) magnetic nanoparticles and to investigate their sorption characteristics towards Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺ ions in aqueous solution. MgFe₂O₄ was synthesized by glycine-nitrate combustion method and was characterized by low crystallinity with crystallite size of 8.2?nm, particle aggregates of 13–25?nm, BET surface area of 14?m²/g and pore size of 8.0?nm. Sorption properties of MgFe₂O₄ towards Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺ ions were studied using one-component model solutions and found to be dependent on metal ions concentration, contact time, pH and conditions of regeneration experiment. The highest sorption capacity of MgFe₂O₄ was detected towards Co²⁺ (2.30?mmol?g¹) and Mn²⁺ (1.56?mmol?g^?1) and the lowest towards Ni²⁺ (0.89?mmol?g^?1) and Cu²⁺ (0.46?mmol?g^?1). It was observed that sorption equilibrium occurs very quickly within 20–60?min. The pH_zpc of sorbent was calculated to be 6.58. At studied pH interval (3.0–7.0) the sorption capacity of MgFe₂O₄ was not significantly affected. Regeneration study showed that the metal loaded sorbent could be regenerated by aqueous solution of 10^?3 M MgCl₂ at pH 6.0 within 120?min of contact time. Regeneration test suggested that MgFe₂O₄ magnetic sorbent can be efficiently used at least for four adsorption-desorption cycles. The high sorption properties and kinetics of toxic metal ion sorption indicates good prospects of developed sorbent in practice for wastewater treatment.     

Electrochemical properties and structural characterization of layered Li[Ni0.5Mn0.5]O2 cathode materials

Layered Li[Ni_0.5Mn_0.5]O₂ materials with high homogeneity and crystallinity were prepared using high speed ball milling. The Li[Ni_0.5Mn_0.5]O₂ electrode delivered a high discharge capacity of 152 mA h g⁻¹ between 2.8 and 4.3 V with excellent cycleability. The TEM analysis showed that the Li[Ni_0.5Mn_0.5]O₂ electrode went through a considerable morphological change without altering its initial layered structure while the electrode retained its initial discharge capacity even after 50 cycles.     

Optimal synthesis and new understanding of P2-type Na2/3Mn1/2Fe1/4Co1/4O2 as an advanced cathode material in sodium-ion batteries with improved cycle stability

A sol-gel method with ethylene diamine tetraacetic acid and citric acid as co-chelates is employed for the synthesis of P2-type Na_2/3Mn_1/2Fe_1/4Co_1/4O₂ as cathode material for sodium-ion batteries. Among the various calcination temperatures, the Na_2/3Mn_1/2Fe_1/4Co_1/4O₂ with a pure P2-type phase calcined at 900 °C demonstrates the best cycle capacity, with a first discharge capacity of 157 mA h g^?1 and a capacity retention of 91 mA h g^?1 after 100 cycles. For comparison, the classic P2-type Na_2/3Mn_1/2Fe_1/2O₂ cathode prepared under the same conditions shows a comparable first discharge capacity of 150 mA h g^?1 but poorer cycling stability, with a capacity retention of only 42 mA h g^?1 after 100 cycles. Based on X-ray photoelectron spectroscopy, the introduction of cobalt together with sol-gel synthesis solves the severe capacity decay problem of P2-type Na_2/3Mn_1/2Fe_1/2O₂ by reducing the content of Mn and slowing down the loss of Mn on the surface of the Na_2/3Mn_1/2Fe_1/4Co_1/4O₂, as well as by improving the activity of Fe³⁺ and the stability of Fe⁴⁺ in the electrode. This research is the first to demonstrate the origin of the excellent cycle stability of Na_2/3Mn_1/2Fe_1/4Co_1/4O₂, which may provide a new strategy for the development of electrode materials for use in sodium-ion batteries.     

Synthesis optimization of Li1 + x[Mn0.45Co0.40Ni0.15]O2 with different spherical sizes via co-precipitation

Li_1 + x[Mn_0.45Co_0.40Ni_0.15]O₂ spherical cathode materials with different sizes (about 2 and 5 μm) were fabricated by calcining uniform spherical metal carbonate, [Mn_0.45Co_0.40Ni_0.15]CO₃ with lithium hydroxide at high temperature. The precursor of spherical metal carbonate, [Mn_0.45Co_0.40Ni_0.15]CO₃, was obtained via co-precipitation method at room temperature, which was significantly dependent on synthetic conditions, such as the reaction temperature, the concentration of NH₄HCO₃, and stirring speed, etc. The optimized condition resulted in [Mn_0.45Co_0.40Ni_0.15]CO₃, of which the particle size distribution was uniform and the particle shape was spherical. The final products, Li_1 + x[Mn_0.45Co_0.40Ni_0.15]O₂, had a well-ordered layered structure and uniform homogeneity. Raman spectroscopy analysis showed the Raman-active species E_g and A_1g modes were observed at 488, 473 cm^− 1 and 597, 590 cm^− 1, respectively, for the obtained spherical cathode materials.     

A simple and effective method to synthesize layered LiNi0.8Co0.1Mn0.1O2 cathode materials for lithium ion battery

Nanocrystalline materials of Ni_0.8Co_0.1Mn_0.1(OH)₂ are successfully synthesized by fast co-precipitation method. The crystalline structure and morphology of the precursors and LiNi_0.8Co_0.1Mn_0.1O₂ materials are characterized by XRD, SEM and Rietveld refinement analyses. It is found that the nanocrystalline phase and low crystallinity of Ni_0.8Co_0.1Mn_0.1(OH)₂ could help achieve its uniform mixing with lithium source, and further attribute to highly ordered layered LiNi_0.8Co_0.1Mn_0.1O₂ with low cation mixing degree. Electrochemical studies confirm that the LiNi_0.8Co_0.1Mn_0.1O₂ exhibits a good electrochemical property with initial discharge specific capacity of 192.4 mAh g^− 1 at a current density of 18 mA g^− 1, and the capacity retention after 40 cycles is 91.56%. This method is a simple and effective method to synthesize cathode material.     

Synthesis and characterization of Mo-doped LiNi0.5Co0.2Mn0.3O2 cathode materials prepared by a hydrothermal process

The lithiated metal oxide precursor with α-NaFeO₂ structure and low crystallinity prepared by a hydrothermal process is verified to be Li-Ni-Co-Mn-Mo composite oxide. The layered Li(Ni_0.5Co_0.2Mn_0.3)_1-xMo_xO₂ (x=0, 0.005, 0.01 and 0.02) cathode material with high crystallinity for lithium ion batteries (LIBs) is obtained from the lithiated metal oxide precursor by heat treatment. The results of SEM and EDS mapping characterization indicate that the molybdenum is distributed in the materials homogeneously. The effects of molybdenum on the structure, morphology and electrochemical performances of the LiNi_0.5Co_0.2Mn_0.3O₂ are extensively studied. According to the results of electrochemical characterizations, the Li(Ni_0.5Co_0.2Mn_0.3)_0.99Mo_0.01O₂ sample exhibits the best discharge cycling performance with capacity retention of 97.0% after 50 cycles, and an excellent rate performance of 125.5 mAh·g⁻¹ at 8C rate. The Li(Ni_0.5Co_0.2Mn_0.3)_0.99Mo_0.01O₂ sample also shows a lower potential polarization, smaller impedance parameters and a larger Li⁺ diffusion by CV and EIS analyses.     

Carbon-coated Bi5Nb3O15 as anode material in rechargeable batteries for enhanced lithium storage

Bismuth can alloy with lithium to generate Li₃Bi with the volumetric capacity of about 3765 mAh cm^?3 (386 mAh g^?1), rendering bismuth-based materials as attractive alloying-type electrode materials for rechargeable batteries. In this work, bismuth-based material Bi₅Nb₃O₁₅ @C is fabricated as anode material through a traditional solid-state reaction with glucose as carbon source. Bi₅Nb₃O₁₅ @C composite is well dispersed, with small particle size of 0.5–2.0?µm. The electrochemical performance of Bi₅Nb₃O₁₅ @C is reinforced by carbon-coated layer as desired. The Bi₅Nb₃O₁₅ @C exhibits a high specific capacity of 338.56 mAh g^?1 at a current density of 100?mA?g^?1. And it also presents an excellent cycling stability with a capacity of 212.06 mAh g^?1 over 100 cycles at 100?mA?g^?1. As a comparison, bulk Bi₅Nb₃O₁₅ without carbon-coating only remains 319.62 mAh g^?1 at 100?mA?g^?1, revealing poor cycle and rate performances. Furthermore, in-situ X-ray diffraction experiments investigate the alloying/dealloying behavior of Bi₅Nb₃O₁₅ @C. These insights will benefit the discovery of novel anode materials for lithium-ion batteries.     

High-voltage performance of concentration-gradient Li[Ni0.67Co0.15Mn0.18]O2 cathode material for lithium-ion batteries

A novel Li[Ni_0.67Co_0.15Mn_0.18]O₂ cathode material encapsulated completely within a concentration-gradient shell was successfully synthesized via co-precipitation. The Li[Ni_0.67Co_0.15Mn_0.18]O₂ has a core of Li[Ni_0.8Co_0.15Mn_0.05]O₂ that is rich in Ni, a concentration-gradient shell having decreasing Ni concentration and increasing Mn concentration toward the particle surface, and a stable outer-layer of Li[Ni_0.57Co_0.15Mn_0.28]O₂. The electrochemical and thermal properties of the material were investigated and compared to those of the core Li[Ni_0.8Co_0.15Mn_0.05]O₂ material alone. The discharge capacity of the concentration-gradient Li[Ni_0.67Co_0.15Mn_0.18]O₂ electrode increased with increasing upper cutoff voltage to 4.5 V, and cells with this cathode material delivered a very high capacity, 213 mAh/g, with excellent cycling stability even at 55 °C. The enhanced thermal and lithium intercalation stability of the Li[Ni_0.67Co_0.15Mn_0.18]O₂ was attributed to the gradual increase in tetravalent Mn concentration and decrease in Ni concentration in the concentration-gradient shell layer.     

Improved electrochemical properties of Li1.2Ni0.18Mn0.59Co0.03O2 by surface modification with LiCoPO4

Lithium-rich nickel–manganese–cobalt oxide, Li_1.2Ni_0.18Mn_0.59Co_0.03O₂, prepared by spray-dry process, exhibits rapid capacity fade and poor rate capability. The surface of Li_1.2Ni_0.18Mn_0.59Co_0.03O₂ can be modified with LiCoPO₄ through co-precipitation method in order to improve its electrochemical properties. The resultant LiCoPO₄ particles are in nano-scale and accumulate on the surface of the Li_1.2Ni_0.18Mn_0.59Co_0.03O₂ particles. The surface modification by LiCoPO₄ is shown to significantly improve both the cyclic performance and the rate capability of Li_1.2Ni_0.18Mn_0.59Co_0.03O₂.     

Performance of LiNi1/3Co1/3Mn1/3O2 prepared from spent lithium-ion batteries by a carbonate co-precipitation method

Spherical LiNi_1/3Co_1/3Mn_1/3O₂ cathode particles were resynthesized by a carbonate co-precipitation method using spent lithium-ion batteries (LIBs) as a raw material. The physical characteristics of the Ni_1/3Co_1/3Mn_1/3CO₃ precursor, the (Ni_1/3Co_1/3Mn_1/3)₃O₄ intermediate, and the regenerated LiNi_1/3Co_1/3Mn_1/3O₂ cathode material were investigated by laser particle-size analysis, scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS), thermogravimetry–differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), inductively coupled plasma–atomic emission spectroscopy (ICP-AES), and X-ray photoelectron spectroscopy (XPS). The electrochemical performance of the regenerated LiNi_1/3Co_1/3Mn_1/3O₂ was studied by continuous charge–discharge cycling and cyclic voltammetry. The results indicate that the regenerated Ni_1/3Co_1/3Mn_1/3CO₃ precursor comprises uniform spherical particles with a narrow particle-size distribution. The regenerated LiNi_1/3Co_1/3Mn_1/3O₂ comprises spherical particles similar to those of the Ni_1/3Co_1/3Mn_1/3CO₃ precursor, but with a narrower particle-size distribution. Moreover, it has a well-ordered layered structure and a low degree of cation mixing. The regenerated LiNi_1/3Co_1/3Mn_1/3O₂ shows an initial discharge capacity of 163.5 mA h g^?1 at 0.1 C, between 2.7 and 4.3 V; the discharge capacity at 1 C is 135.1 mA h g^?1, and the capacity retention ratio is 94.1% after 50 cycles. Even at the high rate of 5 C, LiNi_1/3Co_1/3Mn_1/3O₂ delivers the high capacity of 112.6 mA h g^?1. These results demonstrate that the electrochemical performance of the regenerated LiNi_1/3Co_1/3Mn_1/3O₂ is comparable to that of a cathode synthesized from fresh materials by carbonate co-precipitation.     

Preparation of LiNi1/3Co1/3Mn1/3O2/polytriphenylamine cathode composites with enhanced electrochemical performances towards reversible lithium storage

A series of LiNi_1/3Co_1/3Mn_1/3O₂/polytriphenylamine composites were successfully synthesized by ultrasound dispersion method. LiNi_1/3Co_1/3Mn_1/3O₂/polytriphenylamine (5.0?wt%) composite with small and homogeneous particle size exhibited excellent electrochemical performance, which delivered an initial discharge capacity of 223.7?mAh g^?1 with a capacity retention of 84.39% after 100 cycles in the voltage range of 2.5–4.5?V and at a current density of 0.2C. Moreover, an excellent specific discharge capacity of 127.3?mAh g^?1 at a current density 5C indicates a superior rate performance of the LiNi_1/3Co_1/3Mn_1/3O₂/polytriphenylamine (5.0?wt%) composite. The good electrochemical performances of the composite can be attributed to the introduction of polytriphenylamine, which increased electrical conductivity, decreased charge transfer resistance and increased Li⁺ ion diffusion ability. These noteworthy results demonstrated that LiNi_1/3Co_1/3Mn_1/3O₂/polytriphenylamine composites might be potential cathode materials for lithium ion batteries.     

A comparison of preparation method on the electrochemical performance of cathode material Li[Li0.2Mn0.54Ni0.13Co0.13]O2 for lithium ion battery

Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ as a cathode material for Li-ion battery has been successfully prepared by co-precipitation (CP), sol–gel (SG) and sucrose combustion (SC) methods. The prepared materials were characterized by XRD, SEM, BET and electrochemical measurements. The XRD result shows that the Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ materials prepared by different methods all form a pure phase with good crystallinity. SEM images and BET data present that the SC-material exhibited the smallest particle size (ca. 0.1 μm) and the highest surface area (7.4635 m² g⁻¹). The tap density of SC-material is lower than that of CP- and SG-materials. The result of rate performance tests indicates that the SC-material showed the best rate capability with the highest discharge capacity of 178 mAh g⁻¹ at 5.0 C, followed by SG-material and then CP-material. However, the cycling stability of SC-material tested at 0.1 and 0.5 C is relatively poor as compared to that of SG-material and CP-material. The result of EIS measurements reveals that large surface area and small particle size of the SC-electrode result in more SEI layer formation because of the increased side reactions with the electrolyte during cycling, which deteriorates the electrode/electrolyte interface and thus leads to the faster capacity fading of the SC-material.     

High-rate, high capacity ZrO2 coated Li[Li1/6Mn1/2Co1/6Ni1/6]O2 for lithium secondary batteries

Recently, there have been many reports on efforts to improve the rate capability and discharge capacity of lithium secondary batteries in order to facilitate their use for hybrid electric vehicles and electric power tools. In the present work, we present a ZrO₂-coated Li[Li_1/6Mn_1/2Co_1/6Ni_1/6]O₂. The bare Li[Li_1/6Mn_1/2Co_1/6Ni_1/6]O₂ shows a high initial discharge capacity of 224 mAh g⁻¹ at a 0.2 C rate. Owing to the stability of ZrO₂, it was possible to enhance the rate capability and cyclability. After 1 wt% ZrO₂ coating, the ZrO₂-coated Li[Li_1/6Mn_1/2Co_1/6Ni_1/6]O₂ showed a high discharge capacity of 115 mAh g⁻¹ after 50 cycles under a 6 C rate, whereas the bare Li[Li_1/6Mn_1/2Co_1/6Ni_1/6]O₂ showed a discharge capacity of only 40 mAh g⁻¹ and very poor cyclability under the same conditions. Based on results of XRD and EIS measurements, it was found that the ZrO₂ suppressed impedance growth at the interface between the electrodes and electrolyte and prevented collapse of the layered hexagonal structure.     

Effect of Cationic (Na+) and Anionic (F−) Co-Doping on the Structural and Electrochemical Properties of LiNi1/3Mn1/3Co1/3O2 Cathode Material for Lithium-Ion Batteries

Elemental doping for substituting lithium or oxygen sites has become a simple and effective technique to improve the electrochemical performance of layered cathode materials. Compared with single-element doping, this work presents an unprecedented contribution to the study of the effect of Na⁺/F⁻ co-doping on the structure and electrochemical performance of LiNi_1/3Mn_1/3Co_1/3O₂. The co-doped Li_1-zNa_zNi_1/3Mn_1/3Co_1/3O_2-zF_z (z = 0.025) and pristine LiNi_1/3Co_1/3Mn_1/3O₂ materials were synthesized via the sol–gel method using EDTA as a chelating agent. Structural analyses, carried out by X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy, revealed that the Na⁺ and F⁻ dopants were successfully incorporated into the Li and O sites, respectively. The co-doping resulted in larger Li-slab spacing, a lower degree of cation mixing, and the stabilization of the surface structure, which substantially enhanced the cycling stability and rate capability of the cathode material. The Na/F co-doped LiNi_1/3Mn_1/3Co_1/3O₂ electrode delivered an initial specific capacity of 142 mAh g⁻¹ at a 1C rate (178 mAh g⁻¹ at 0.1C), and it maintained 50% of its initial capacity after 1000 charge–discharge cycles at a 1C rate.