Electrochemical Performance Of LiCoO Research Articles

Improved thermal stability of lithium ion battery by using cresyl diphenyl phosphate as an electrolyte additive

To enhance the safety of lithium ion battery, cresyl diphenyl phosphate (CDP) is explored as an additive in 1.0 M LiPF 6/ethylene carbonate (EC) + diethyl carbonate (DEC) (1:1 wt.). The electrochemical performances of LiCoO 2/CDP-electrolyte/C cells are tested. At the thermal aspect, the thermal stability of the electrolyte with CDP is detected firstly by using a C80 micro-calorimeter, and then the charged LiCoO 2/CDP-electrolyte/C cells are disassembled and wrapped to detect the thermal behaviors. The results indicate that CDP-containing electrolyte enhances the thermal stabilities of electrolyte and lithium ion battery, and the electrochemical performances of LiCoO 2/CDP-electrolyte/C cell become slightly worse by using CDP in the electrolyte. Furthermore, the cell with 10% (wt.) CDP-containing electrolyte shows better cycle efficiency than that of other CDP-containing electrolyte, such as containing 5% (wt.) CDP and 15% (wt.) CDP. This maybe because that the mass ratio between CDP and electrolyte is close to the reaction stoichiometric ratio in the 10% (wt.) CDP-containing electrolyte, where stable solid electrolyte interphase (SEI) is formed. Therefore, 10% CDP-containing electrolyte improves the safety of lithium ion battery and keeps its electrochemical performance.

Effect of slurry preparation process on electrochemical performances of LiCoO 2 composite electrode

The slurries comprising LiCoO 2 powder, carbon, and polymeric binder are prepared by two different mixing processes, and their rheological properties are compared. In the multi-step process, the solvent is added into solid mixture in stepwise, whereas the total amount at once in the one-step process. The former process gives the slurry that is more suitable for electrode preparation with fluid-like behavior and more uniform dispersion of solid ingredients as compared to those prepared from the letter. In the composite electrode prepared from the former, the LiCoO 2 and carbon particles are homogeneously distributed without agglomeration. Indebted to this favorable feature, this electrode exhibits a better electrochemical performance for cyclability and rate capability. It is very likely that the contact resistance and charge transfer resistance for lithiation/de-lithiation are smaller in the former electrode due to the homogeneous distribution of LiCoO 2 and carbon particles, which leads to a less significant electrode polarization.

Effects of SrO/Li 2O/La 2O 3/Ta 2O 5/TiO 2-coating on electrochemical performance of LiCoO 2

Commercial cathode material (LiCoO 2) was modified by coating with a thin layer of SrO/Li 2O/La 2O 3/Ta 2O 5/TiO 2 for improving its performance in lithium ion battery. The morphology and structure of the modified cathode material were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The performance including cycling stability, diffusion coefficient under different voltage, C-rate discharge of the batteries with this modified cathode material was examined. The results showed that the battery with the coated cathode material could discharge at a large current density, and it possessed a stable cycle performance in the range from 3.0 V to 4.2 V. It was explained that the rate of Li ion diffusion increased in the batteries using SrO/Li 2O/La 2O 3/Ta 2O 5/TiO 2-coated LiCoO 2 as the cathode and the coated layer could act as a fast ion conductor (Sr 0.5La 0.05Li 0.35 Ti 0.5Ta 0.5O 3) and as a protecting shell to prevent LiCoO 2 particles from being attacked by the acidic electrolyte.

Electrochemical performance of LiCoO 2 cathodes by surface modification using lanthanum aluminum garnet

LiCoO 2 particles were coated with various wt.% of lanthanum aluminum garnets (3LaAlO 3:Al 2O 3) by an in situ sol–gel process, followed by calcination at 1123 K for 12 h in air. X-ray diffraction (XRD) patterns confirmed the formation of a 3LaAlO 3:Al 2O 3 compound and the in situ sol–gel process synthesized 3LaAlO 3:Al 2O 3-coated LiCoO 2 was a single-phase hexagonal α-NaFeO 2-type structure of the core material without any modification. Scanning electron microscope (SEM) images revealed a modification of the surface of the cathode particles. Transmission electron microscope (TEM) images exposed that the surface of the core material was coated with a uniform compact layer of 3LaAlO 3:Al 2O 3, which had an average thickness of 40 nm. Galvanostatic cycling studies demonstrated that the 1.0 wt.% 3LaAlO 3:Al 2O 3-coated LiCoO 2 cathode showed excellent cycle stability of 182 cycles, which was much higher than the 38 cycles sustained by the pristine LiCoO 2 cathode material when it was charged at 4.4 V.

Effects of La 2O 3/Li 2O/TiO 2-Coating on Electrochemical Performance of LiCoO 2 Cathode

Conventional cathode material (LiCoO 2) was modified by coating with a thin layer of La 2O 3/Li 2O/TiO 2 for improving its performance for lithium ion battery. The morphology and structure of the modified cathode material was characterized by SEM, XRD, and Auger electron spectroscopy. The performance of the cells with the modified cathode material was examined, including the cycling stability, the diffusion coefficient under different voltages, and the C-rate discharge. The results showed that the cell composed of the coated cathode material discharged at a large current density, and possesses a stable cycle performance in the range from 3.0 to 4.4 V. It was explained that the rate of Li ion diffusion increased in the cell while using La 2O 3/Ti 2O/TiO 2-coated LiCoO 2 as the cathode and the coating layer may act as a faster ion conductor (La 2O 3/Ti 2O/TiO 2).

Effect of LiFePO 4 coating on electrochemical performance of LiCoO 2 at high temperature

LiFePO 4 coating on LiCoO 2 with a thickness ranging 10–100 nm improved the electrochemical performance of the cathode material at high temperature and high potential. At 60 °C and at a rate of 1 C, 5.0 wt.% LiFePO 4-coated LiCoO 2 showed better capacity retention (132 mAh/g) with 4.2 V charge-cutoff after 250 cycles, while the bare cathode (pure LiCoO 2) showed 5% capacity retention under the same conditions after only 150 cycles. When cycled at 60 and 75 °C, the amount of Co dissolution from LiCoO 2 was greatly reduced in the LiFePO 4-coated cathode material. The coating layer of LiFePO 4 not only protects the LiCoO 2 but also serves as an active cathode material with good conductivity. The LiFePO 4-coated LiCoO 2 could be a high performance cathode material for Li-ion battery.

Enhancing the safety of lithium ion batteries by 4-isopropyl phenyl diphenyl phosphate

To enhance the safety of lithium ion batteries, 4-isopropyl phenyl diphenyl phosphate (IPPP) was explored as an additive in 1.0 M LiPF 6/ethylene carbonate (EC) + diethyl carbonate (DEC) (1:1 wt.%). The electrochemical performances of LiCoO 2/IPPP electrolyte/C cells were tested. And then the LiCoO 2/IPPP electrolyte/C cells were disassembled and wrapped to detect the thermal behaviors using a C80 microcalorimeter. The results indicated that 5% and 10% IPPP content in the electrolyte can enhance the safety of lithium ion batteries. Furthermore, the electrochemical performances of LiCoO 2/IPPP electrolyte/C cells become slightly worse by using 5% and 10% IPPP content electrolyte. Therefore, 5–10% IPPP content in electrolyte can enhance the safety of lithium ion batteries with minimum sacrifice in electrochemical performance.

Enhancing the thermal stability of LiCoO 2 electrode by 4-isopropyl phenyl diphenyl phosphate in lithium ion batteries

To enhance the thermal stability of LiCoO 2 in lithium ion batteries, 4-isopropyl phenyl diphenyl phosphate (IPPP) was investigated as an additive in 1.0 M LiPF 6/EC + DEC (1:1 wt.%) electrolyte. The thermodynamics and kinetics parameters of the single LiCoO 2 and Li x CoO 2–IPPP-electrolyte are detected and calculated based on the C80 microcalorimeter data. The results indicated that IPPP can enhance the thermal stability of LiCoO 2 electrode in lithium ion battery more or less corresponding to the IPPP content in electrolyte. Furthermore, the electrochemical performances of LiCoO 2/IPPP-electrolyte/Li cells become slightly worse after using IPPP additive in the electrolyte. This alleviated trade-off between thermal stability and cell performance provides a possibility to formulate an electrolyte containing 5–10% of IPPP and enhance the LiCoO 2 electrode thermal stability with minimum sacrifice in performance.

Electrolyte additive trimethyl phosphite for improving electrochemical performance and thermal stability of LiCoO 2 cathode

The purpose of this paper is to investigate compositions on the interface between LiCoO 2 and electrolyte when trimethyl phosphite TMP(i) is used as an additive in 1 M LiPF 6/EC + DEC electrolyte system and the thermal stability of the electrolyte as well as Li 0.5CoO 2 mixed with the electrolyte. The electrochemical performance of LiCoO 2 electrode in the two electrolyte systems was also studied. It is found that the electrochemical performance, including capacity, cycle performance and 3.6 V plateau efficiency, has been improved in the electrolyte with TMP(i) additive. FTIR analysis indicates that Li x PO y is an important surface film composition on the cathode in TMP(i) containing system. A thicker and more passivating surface layer is formed when using TMP(i) additive as an additive. The thermal stability of the cathode is substantially improved in the electrolyte containing TMP(i) additive in the system, especially the exothermic peak around 190 °C, which is associated with the reaction between active surface of cathode and solvents, is obviously restrained.

The effects of gamma-radiation on lithium-ion cells

Planetary explorations of human beings necessitate the research of the influence of γ-radiation on lithium-ion cells. In this study, the radioactive Co-60 was used as the radiation source. The electrochemical performances of LiCoO 2/graphite full cells and LiCoO 2/Li half-cells with a LiPF 6-based electrolyte were measured before and after the radiation. The structural and compositional changes of the cell components were evaluated by means of X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR), and 1H nuclear magnetic resonance spectroscopy ( 1H NMR). The experimental results indicate that the cell performance is substantially deteriorated after the radiation due to two aspects of changes, i.e. radiation-induced defects in LiCoO 2 and production of carboxyl in the electrolyte. The cell degradation is more pronounced for the LiCoO 2/C full cells than for LiCoO 2/Li half-cells owing to the reaction between active lithium and the carboxyl.

The negative and positive structural effects of Ga doping in the electrochemical performance of LiCoO 2

The electrochemical performance of LiGa y Co 1− y O 2 electrodes , y = 0.005 and 0.1, was studied. Charge/discharge curves in galvanostatic condition were obtained for a series of voltages ranging from 4.35 to 4.7 V. Samples were previously characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray absorption spectroscopy (XAS) and conductivity measurements. Comparison of data obtained for LiGa y Co 1− y O 2 and the pristine oxide LiCoO 2 is provided. Ga doping at 0.5 mol% drastically reduces the electrode capacity fading when charges at 4.35 or 4.5 V are applied, while Ga doping at 10 mol% spoils the Ga-doped oxides electrochemical response, even at a cut-off limit of 4.35 V. These positive and negative effects were attributed to changes in both the electronic conductivity and local structure of LiCoO 2, induced by substitution of Co for Ga and cationic disorder. For y = 0.005, a slight distortion in the LiCoO 2 local structure occurs, and formation of states in the band gap that the raise oxide electronic conductivity is observed, explaining the electrochemical improvement in LiGa y Co 1− y O 2. In contrast, hybridization with oxygen occurs when y = 0.1, opening LiCoO 2 band gap and making LiGa y Co 1− y O 2 an insulator and a cationic disorder material that leads to poor electrochemical performance. Finally, XAS results show that Ga doping does not change the LiCoO 2 charge transfer mechanisms, where oxygen is reduced during lithium extraction.

LiCoO 2 cathode material coated with nano-crystallized ZnO for Li-ion batteries

LiCoO 2 is the most widely used cathode material for Li-ion batteries. However, the structural changes and cobalt dissolution into the electrolyte during cycling will lead to rapid capacity fading. Recently, surface modification of the cathode material with metal oxides is found to be a potential approach to improve the electrochemical properties. In this study, nano-crystallized ZnO was coated on the surface of LiCoO 2 powders via a wet chemical method. The influence of the amount of coated ZnO on cycling behavior of surface-treated LiCoO 2 powders was discussed. Moreover, the effect of the pristine-modified powders on the structural properties was also evaluated. The surface morphology characterization was achieved by scanning electron microscope (SEM). Nano-crystallined ZnO was clearly observed on the surfaces of LiCoO 2 particles. The phase and structural changes of the cathode materials before and after coating were revealed by X-ray diffraction (XRD). It was discovered that LiCoO 2 cathodes deposited with different amount of ZnO exhibited distinct surface morphology and lattice constants. From the correlation between these characteristics of bare and coated LiCoO 2 powders, the role of ZnO coating played on the electrochemical performance of LiCoO 2 was probed.

Impacts of Electrolyte Solvent Soakage on Structure and Electrochemical Performance of LiCoO[sub 2] for Lithium-Ion Batteries

Commercial LiCoO2 for lithium-ion batteries is high-energy ball-milled to nanoscale sizes. Bare and Al2O3-coated nano- LiCoO2 particles are soaked in a mixture of ethylene carbonate and dimethyl carbonate. The influences of solvent soakage on the structure and electrochemical performance of the material are characterized with X-ray diffraction, Raman spectroscopy, scanning electron microscopy, inductively coupled plasma technique, and galvonostatic electrochemical cycling. It is shown that solvent soakage has significant impact on the structure and electrochemical properties of bare and Al2O3-coated LiCoO2 positive electrode materials. (C) 2004 The Electrochemical Society.

Influence of chemical prehistory on the phase formation and electrochemical performance of LiCoO 2 materials

Thermal decomposition of freeze-dried salt precursors leads to the formation of low-temperature (LT) modification of LiCoO 2 at 350–450 °C. The conversion rate of LT into high-temperature (HT) modification at 850 °C depends greatly on the anion composition of salt precursors and correlates quite well with the appearance of second step at thermogravimetric curves of their thermal decomposition related to the solid-state reaction between Li 2CO 3 and Co 3O 4. Relationship between the appearance of Co 3O 4 and preferential formation of LT/HT polymorphs at reduced temperatures is discussed. The consecutive formation of LT and HT modifications during solid-state reaction between Li 2CO 3 and Co 3O 4 at T>800 °C was observed. LiCoO 2 cathode materials with the domination of LT polymorph demonstrated a better initial discharge capacity while a greater amount of HT modification is accompanied by better reversibility of charge–discharge processes.

Effect of carbon additive on electrochemical performance of LiCoO 2 composite cathodes

LiCoO 2 composite electrodes are prepared with variation in the conducting agent and their cathodic performance is analyzed. Two carbon blacks (Super P and acetylene black) and one graphite (Lonza KS6) that differ in particle size and shape are employed as the conducting agents. The carbon blacks comprise nano-sized primary particles that are fused to give an aggregate. Lonza KS6 carries a flake-like shape with an average particle size of 6 μm, which is comparable with that of LiCoO 2 particles. The LiCoO 2 composite cathode containing Lonza KS6 exhibits better cycle performance than that of the cathode loaded with carbon black, presumably due to a more uniform dispersion of both the conducting agent and the LiCoO 2 active material. Better mixing in the slurry preparation step that is due to a similarity in the grain size of Lonza KS6 and LiCoO 2 may explain this feature. In composite cathodes containing the smaller-sized carbon blacks, however, the carbon particles agglomerate by themselves to become segregated from the LiCoO 2-rich region. The cathode capacity and cycle-life of a Lonza KS6 loaded electrode is improved further by adding smaller-sized carbon blacks as the conducting agents. It is expected that the smaller particles of carbon black fill the void spaces made by the larger-sized Lonza KS6 and LiCoO 2 grains. As a result, both the electrode conductivity and active surface-area of the LiCoO 2|carbon interface are enlarged. This leads to a decrease in the electrode polarization and a better utilization of the active material.

Effects of conducting carbon on the electrochemical performance of LiCoO 2 and LiMn 2O 4 cathodes

The effects of conducting carbon additive on the performance of LiCoO 2 and LiMn 2O 4 cathodes in lithium-ion batteries have been investigated. While 2–5 wt.% of carbon are adequate for the LiMn 2O 4 cathode to deliver good rate capability and maintain cyclability, the LiCoO 2 cathode requires more carbon (10 wt.%) to achieve likewise. The sensitivity of the LiCoO 2 electrode for carbon content is particularly pronounced in high rate charging. Cyclic voltammetry and electrochemical impedance spectroscopy measurements indicate that deteriorating particle contacts leading to the incomplete charging of the active materials is the primary cause of material non-performance.

Study on the Structure and Electrochemical Performances of LiCoO<sub>2</sub> Dopped with Ni<sup>2+</sup>

Study on the Structure and Electrochemical Performances of LiCoO<sub>2</sub> Dopped with Ni<sup>2+</sup>