Electrochemical Performance Of LiCoO2 Research Articles

Characterization of Garnet-Type Li6SrLa2Bi2O12 Solid Electrolyte for LiCoO2 Cathode Composite in All-Solid-State Battery

Together with the development of inorganic solid lithium (Li) ion conducting materials for the use as solid electrolytes, the formation of intimate solid-solid interface between electrode active material and solid electrolyte is pivotal for realizing high performance all-solid-state Li-ion batteries (LiBs) with high safety and reliability. Oxide-based solid electrolytes have the advantages of good chemical stability and ease of handling, but for many of them, the high temperature processing is required for the densification, which may cause undesired side reactions with electrode active materials during the processing.Although garnet-type oxide solid electrolyte Li6SrLa2Bi2O12 (LSLBO) has lower ionic conductivity than widely studied garnet-type Li7La3Zr2O12 (LLZO), LSLBO can be sintered at much lower temperatures than LLZO [1,2]. Therefore, there is a possibility to suppress the side reaction with electrode active materials during high-temperature sintering for fabricating oxide-based all-solid-state LiBs.In this study, we prepared dense LSLBO or composites of LiCoO2 (LCO) cathode and LSLBO by hot pressing (HP). LSLBO densified at 750 °C for 1 hour showed high relative density of 95%. The densification temperature of LSLBO by HP confirmed in this work is 100–150 °C lower than Bi-doped LLZO with the formula of Li6La3ZrBiO12 (LLZBO) [3, 4]. Bulk and total (bulk + grain conductivity) ionic conductivity of LSLBO fabricated by HP attained to 2.1 × 10-4 and 1.1 × 10-4 S/cm at room temperature, which is much higher than LSLBO prepared by a conventional furnace sintering (FS) [1] and spark plasma sintering (SPS) [2]. The electrochemical stability of LSLBO at an electrical potential from 3 to 6 V vs. Li/Li+ was also confirmed by measuring the cyclic voltammogram.From XRD analysis of mixed LSLBO and LCO powders after annealing, LSLBO and LCO were found to be thermally compatible at temperature below 800 °C and LCO-LSLBO composite densified at 700 °C for 1 hour by HP showed mixed conducting properties with both electronic and ionic conductivity of 10-5-10-4 S/cm at room temperature. From galvanostatic charge and discharge testing of sintered LCO-LSLBO composite sheet, we found that electrochemical performance of LCO is not degraded by co-sintering with LSLBO. These results suggest that LSLBO solid electrolyte can be applied for LCO cathode composite in oxide-based all-solid-state LiBs.

Unraveling the Distinct Roles of Mg Occupation on Li or Co Sites on High-Voltage LiCoO2

A high-voltage LiCoO2 cathode material has been increasingly studied due to its high capacity; however, the structural instability of this material results in poor cycling performance at high voltages, restricting its application. We use a controlled Mg doping strategy to modulate the crystal and electronic structure of the material and unravel the different effects of Mg occupation at Li and Co sites on the structure and electrochemical performance of LiCoO2. Mg substitution at Li sites provides much better electrochemical performance than Mg substitution at Co sites. Compared with bare LiCoO2, the substitution of Mg for Li and Co significantly enhances the capacity retention from 0.5% to 58.6% and 85.6% (500 cycles at 5C), respectively. Mg substitution at Li sites provides a “pillar’ to stabilize the layered structure and increases the interlayer spacing (I(LiO2)) to reduce the energy barrier for Li+ migration. The stress and strain on the crystal structure caused by the substantial expansion and contraction during cycling are alleviated, while the stability of oxygen in the Li0.96Mg0.04CoO2 sample is enhanced; additionally, the destruction of the CoO6 octahedron is also significantly inhibited, all of which confirm the increase in stabilization due to the Mg substitution in LiCoO2. This study offers some insights on the distinct effects of the same dopant at different crystal sites, which is instructive to develop a precisely controlled doping strategy.

Study on the formation, development and coating mechanism of new phases on interface in LiNbO3-coated LiCoO2

Surface coating is one of important methods to improve the electrochemial performances of cathode material for Li-ion batteries. Few work focuses on whether the “the formed coating surface” is “the chosen coating surface” or not. In this study, it has been found that bulk material LiCoO2 (LCO) and the LiNbO3 coating material can react to produce Li3NbO4 and Co3O4 and form new coating layers during heating. The development of the new coating layers after calcination and their effect on the electrochemical performance of LiCoO2 have been thoroughly studied. Different types of coating layers (LiNbO3, LiNbO3/Li3NbO4/Co3O4, Li3NbO4/Co3O4 coating layers) were designed and obtained. The formation of new coating layer played a vital role in improving the electrochemical properties of coated materials. Coated LCO obtained at 650 oC with a LiNbO3/Li3NbO4/Co3O4 new coating layer exhibited the most excellent cycle stability with a capacity retention of 94.3% after 100 cycles at 0.2 C. The coating mechanism was studied. Both the composition and coating surface structure affect the performances of coated LCO. LiNbO3/Li3NbO4/Co3O4-coated LCO had the most uniform and integrated coating layer, maintained well crystal structure after long-term charging-discharging process. In addition, the LiNbO3/Li3NbO4/Co3O4 coating layer has been proved to inhibit the growth of cathode electrolyte interface.

Determining the intrinsic role of Mg doping in LiCoO2

The electrochemical performance of LiCoO2 can be substantially improved via multielemental doping to enable high-voltage applications. However, the limitations and the intrinsic functions of each element in doping have not been identified to date. In this study, we employed commercial LiCoO2 samples and identified Mg doping limitations in Al, Ti, and Mg tri-elemental-doped materials. The results demonstrate that excessive Mg doping is unfavorable to the dynamics of LiCoO2 due to the formation of a ~ 2 nm MgO coating layer and randomly distributed MgO islands, which directly resulted in a decrease of the discharge plateau. Calculations demonstrated the functions of Mg doping and MgO coating. To the best of our knowledge, this report is the first to describe a comprehensive study on the intrinsic role of Mg doping in commercial LiCoO2.

Preparation of Li4Ti5O12/carbon nanotubes composites and LiCoO2/Li4Ti5O12 full-cell with enhanced electrochemical performance for high-power lithium-ion batteries

Through utilizing a facile solid-state sand-milling method, Li4Ti5O12/carbon nanotubes composites containing different quantities of carbon nanotubes were prepared. A series of characterizations detail the ways in which carbon nanotubes have affected grain morphology and electrochemical properties. It is clearly seen from scanning-electron-microscopy images that the carbon nanotubes have uniformly distributed around the Li4Ti5O12 particles and Li4Ti5O12/carbon nanotubes particles are smaller than that of pure Li4Ti5O12. The Li4Ti5O12/carbon nanotubes composite with 4.94 wt% carbon nanotubes (denoted as LTO-CNTs-2) exhibits excellent charge capacities at high C-rates (148.3 mAh g−1 at 20 C, 142.6 mAh g−1 at 30 C) and possesses an outstanding cycling performance with a charge capacity of 138.6 mAh g−1 and a capacity retention of 90.2% at 10 C after 900 cycles. Cyclic-voltammetry test indicates that LTO-CNTs-2 exhibits a larger lithium-ion diffusion coefficient (6.53 × 10−10 cm2 s−1) than that of pure Li4Ti5O12 (1.15 × 10−10 cm2 s−1). Electrochemical-impedance spectra curves also show that LTO-CNTs-2 delivers the smallest charge-transfer resistance (61.0 Ω) among all samples. The electrochemical performance of LiCoO2 (denoted as LCO)/pure Li4Ti5O12 and LCO/LTO-CNTs-2 full cells are investigated. The LCO/LTO-CNTs-2 full-cell exhibits a superior cycling performance with a discharge capacity as high as 143.9 mAh g−1 and a capacity loss of only 4.2% than that of LCO/pure Li4Ti5O12 full-cell at 5 C after 500 cycles, whose discharge capacity is 110.9 mAh g−1 with a capacity loss of 21.8%.

Unraveling the multiple effects of Li2ZrO3 coating on the structural and electrochemical performances of LiCoO2 as high-voltage cathode materials

The poor cycle performance, low rate capability and thermo-instability limit the practical application of LiCoO2 as high-voltage cathode materials for lithium-ion batteries. Herein, we propose an integrated modification strategy which combines the advantages of elements doping, surface modifications and even the high Li+-diffusion of the coating layer. In this study, Li+-conductive Li2ZrO3 has been successfully coated on the surface of LiCoO2 (Li2ZrO3@LCO) through a synchronous lithiation strategy and the multiple effects of Li2ZrO3 coating on the structural and electrochemical performances of LiCoO2 as high-voltage cathode materials for Li-ion batteries have been discovered. In compared to bare LiCoO2, the cycle performance, polarization, rate capability and thermo-stability of Li2ZrO3@LZO have been significantly improved. Li2ZrO3@LCO shows a much higher capacity retention than bare LiCoO2 both at 25°C (85.2% vs.32.6% at 5C, 1C=200mAg−1) and 55°C (71.3% vs.13.9% at 5C), and the specific capacity at 10C has also been largely increased from 33.9mAhg−1 to 103.4mAhg−1. The enhancement of the electrochemical performances can be largely attributed to the multiple effects of Li+-conductive Li2ZrO3 coating: the alleviation of side reactions and transition metal dissolution, the enhancement of Li-ion diffusion coefficient and electronic conductivity, Zr4+ migration and doping, the resulting interplanar spacing expansion and the improvement of the layered structure stability.

Novel application of LiCoO2 as a high-performance candidate material for supercapacitor

Electrochemical performances of LiCoO2 as a candidate material for supercapacitor are systematically investigated. LiCoO2 nanomaterials are synthesized via hydrothermal reaction with consequent calcination process. And the particle size increases as the calcination temperature rises. LCO-650 sample with the largest particle size displays the maximum capacitances of 817.5 F·g−1 with the most outstanding capacity retention rate of 96.8% after 2000 cycles. It is shown that large particle size is beneficial to the electrochemical and structural stability of LiCoO2 materials. We speculate that the micron-sized waste LiCoO2 materials have great potential for supercapacitor application. It may provide a novel recovered approach for spent LIBs and effectively relieve the burdens on the resource waste and environment pollution.

Synergistic Effects of Suberonitrile-LiBOB Binary Additives on the Electrochemical Performance of High-Voltage LiCoO2 Electrodes

Suberonitrile (SUN) and lithium bis(oxalate)borate (LiBOB) were investigated as binary additives for Li-ion batteries that used LiCoO2 as a cathode, cycled at high cutoff potentials and utilized LiPF6-based electrolyte. Linear sweep voltammetry (LSV) results revealed that LiBOB oxidized prior to the decomposition of the reference electrolyte. By contrast, SUN has a higher oxidization potential, and in the electrolyte it provided better electrolyte stability at higher potentials. In the electrolyte with binary additives, the electrochemical performance of LiCoO2 was enhanced significantly, and the initial coulombic efficiency increased to 94% compared with 90% in reference electrolyte. The cell also exhibited capacity retention of 62% after 500 cycles, a strong contrast with the 25% measured in reference electrolyte. Preliminary studies using electrochemical impedance spectra (EIS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analyses indicated that the combination of the two additives had a unique influence on the structure and composition of the cathode-electrolyte interface (CEI) on LiCoO2. Ex situ X-ray diffraction (XRD) confirmed that structural change of the LiCoO2 material was not the main reason causing poor cycling performance when charging to the 4.5 V cutoff potential.

Effect of Al2O3 coating on electrochemical performance of LiCoO2 as cathode materials for secondary lithium batteries

Al2O3-coated LiCoO2 particles are prepared by a gas-suspension spray method with coatings in the range from 0.1 to 2.0 wt.%, and are examined for their electrochemical performance with special attention to the surface coverage of cathode materials for lithium-ion batteries. The Al2O3 coating increases both the surface area and the electrical conductivity of LiCoO2, improves the cycle performance even at a higher cut-off charge voltage, and induces higher thermal stability. In the experimental range studied, different coating amounts (i.e., surface coverage of Al2O3) causes different capacity retention after 50 cycles. The optimum Al2O3 coating amount for the highest capacity retention is 0.2 wt.%. This corresponds to 13.7% of surface coverage.