Synthesis of LiNi1/3Co1/3Mn1/3O2 cathode materials by using a supercritical water method in a batch reactor

LiNi_1/3Co_1/3Mn_1/3O₂ and LiCoO₂ cathode materials were synthesized by using a supercritical water (SCW) method with a metal salt solution in a batch reactor. Stoichiometric LiNi_1/3Co_1/3Mn_1/3O₂ was successfully synthesized in a 10-min reaction without calcination, while overlithiated LiCoO₂ (Li_1.15CoO₂) was synthesized using the batch SCW method. The physical properties and electrochemical performances of LiNi_1/3Co_1/3Mn_1/3O₂ were compared to those of Li_1.15CoO₂ by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and charge/discharge cycling tests. The XRD pattern of LiNi_1/3Co_1/3Mn_1/3O₂ was found to be similar to that of Li_1.15CoO₂, showing clear splitting of the (0 0 6)/(1 0 2) and (1 0 8)/(1 1 0) peak pairs as particular characteristics of the layered structure. In addition, both cathode powders showed good crystallinity and phase purity, even though a short reaction time without calcination was applied to the SCW method. The initial specific discharge capacities of the Li_1.15CoO₂ and LiNi_1/3Co_1/3Mn_1/3O₂ powders at a current density of 0.24 mA/cm² in 2.5-4.5 V were 149 and 180 mAh/g, and their irreversible capacity loss was 20 and 17 mAh/g, respectively. The discharge capacities of the Li_1.15CoO₂ and LiNi_1/3Co_1/3Mn_1/3O₂ powders decreased with cycling and remained at 108 and 154 mAh/g after 30 cycles, which are 79% and 89% of the initial capacities. Compared to the overlithiated LiCoO₂ cathode powders, the LiNi_1/3Co_1/3Mn_1/3O₂ cathode powders synthesized by SCW method had better electrochemical performances.     

Enhanced electrochemical properties of SnO2 anode by AlPO4 coating

A SnO₂ anode material undergoes severe capacity loss, which is mainly associated with cracking/crumbling of the material by the large volume change between the Li_xSn and Sn phases, and the intensive reactions with the electrolyte solution. However, AlPO₄ nanoparticle coating showed drastically improved electrochemical properties with decreased surface cracks. The AlPO₄-coated SnO₂ exhibited a capacity of 781 mAh/g, approaching its theoretical capacity at the first cycle, with 44% capacity retention after 15 cycles between 2.5 and 0 V at a relatively high C rate of 105 mA/g. In contrast, the bare SnO₂ showed an initial capacity of 680 mAh/g, with only 8% capacity retention after 15 cycles.     

Microstructure effect on the electrochemical property of Li4Ti5O12 as an anode material for lithium-ion batteries

Porous (P-) and dense (D-) lithium titanate (Li₄Ti₅O₁₂) powders as an anode material for lithium-ion batteries have been synthesized by spray drying followed by solid-state calcination. Electrochemical testing results showed that the discharge capacities of P-Li₄Ti₅O₁₂ are 144 mAh/g, 128 mAh/g and 73 mAh/g at the discharging rate of 2C, 5C and 20C, respectively (cut-off voltages: 0.5-2.5 V). The corresponding values for D-Li₄Ti₅O₁₂ are 108 mAh/g, 25 mAh/g and 17 mAh/g. The higher capacity of the P-Li₄Ti₅O₁₂ at high charge/discharge rates was attributed to the shorter transport path of Li ions and higher electronic conductivity in the P-Li₄Ti₅O₁₂ as a result of its smaller primary particle size and higher surface area compared with those of the D-Li₄Ti₅O₁₂.     

A study on electrochemical characteristics of LiCoO2/LiNi1/3Mn1/3Co1/3O2 mixed cathode for Li secondary battery

In this study, the LiCoO₂/LiNi_1/3Mn_1/3Co_1/3O₂ mixed cathode electrodes were prepared and their electrochemical performances were measured in a high cut-off voltage. As the contents of LiNi_1/3Mn_1/3Co_1/3O₂ in the mixed cathode increases, the reversible specific capacity and cycleability of the electrode enhanced, but the rate capability deteriorated. On the contrary, the rate capability of the cathode enhanced but the reversible specific capacity and cycleability deteriorated, according to increasing the contents of LiCoO₂ in the mixed cathode. The cell of LiCoO₂/LiNi_1/3Mn_1/3Co_1/3O₂ (50:50, wt.%) mixed cathode delivers a discharge capacity of ca. 168 mAh/g at a 0.2 C rate. The capacity of the cell decreased with the current rate and a useful capacity of ca. 152 mAh/g was obtained at a 2.0 C rate. However, the cell shows very stable cycleability: the discharge capacity of the cell after 20th charge/discharge cycling maintains ca. 163 mAh/g.     

Synthesis and electrochemical properties of submicron LiNi0.8Co0.2O2 by a polymer-pyrolysis method

A polymer-pyrolysis method was used to synthesize LiNi_0.8Co_0.2O₂, which has potential application in lithium ion batteries. The effect of calcination temperature and time on the structure and electrochemical performance of the material was investigated. XRD analysis showed that the powders obtained by calcination at 750 °C for 3 h had the best-ordered hexagonal layer structure. SEM image showed these powders were fine, narrowly distributed with platelet morphology. The charge-discharge tests demonstrated these powders had the best electrochemical properties, with an initial discharge capacity of 189 mAh/g and capacity retention of 95.2% after 50 cycles when cycled at 50 mA/g between 3.0 and 4.3 V. Besides, these powders also had exhibited excellent rate capability.     

Electrochemical properties of carbon-mixed LiFePO4 cathode material synthesized by the ceramic granulation method

LiFePO₄/carbon composite cathode material was prepared using polyvinyl alcohol (PVA) as carbon source by pelleting and subsequent pyrolysis in N₂. The samples were characterized by XRD, SEM and TGA. Their electrochemical performance was investigated in terms of charge–discharge cycling behavior. It consists of a single LiFePO₄ phase and amorphous carbon. The special micro-morphology via the process is favorable for electrochemical properties. The discharge capacity of the LiFePO₄/C composite was 145 mAh/g, closer to the theoretical specific capacity of 170 mAh/g at 0.1 C low current density. At 3 C modest current density, the specific capacity was about 80 mAh/g, which can satisfy for transportation applications if having a more planar discharge flat.     

Mixed oxides Ca2Fe2O5 and Ca2Co2O5 as anode materials for Li-ion batteries

The electrochemical performance of mixed oxides, Ca₂Fe₂O₅ and Ca₂Co₂O₅ for use in Li-ion batteries was studied with Li as the counter electrode. The compounds were prepared and characterized by X-ray diffraction and SEM. Ca₂Fe₂O₅ showed a reversible capacity of 226 mAh/g at the 14th cycle and retained 183 mAh/g at the end of 50 cycles at 60 mA/g in the voltage window 0.005-2.5 V. A reversible capacity in the range, 365-380 mAh/g, which is stable up to 50 charge-discharge cycles is exhibited by Ca₂Co₂O₅ in the voltage window, 0.005-3.0 V and at 60 mA/g. This corresponds to recycleable moles of Li of 3.9±0.1 (theoretical: 4.0). Significant improvement in the cycling performance and attainable reversible capacity were noted for Ca₂Co₂O₅ on cycling to an upper cut-off voltage of 3.0 V as compared to 2.5 V. Coulombic efficiency for both compounds is >98%. Electrochemical impedance spectroscopy (EIS) data clearly indicate the reversible formation/decomposition of polymeric surface film on the electrode surface of Ca₂Co₂O₅ in the voltage window, 0.005-3.0 V. Cyclic voltammetry results compliment the galvanostatic cycling data.     

Carbothermal synthesis, spectral and magnetic characterization and Li-cyclability of the Mo-cluster compounds, LiYMo3O8 and Mn2Mo3O8

The molybdenum cluster compounds, LiYMo₃O₈ and Mn₂Mo₃O₈ are prepared by the carbothermal reduction method and characterized by various techniques. The FT-IR at ambient temperature (RT), and Raman spectra at various temperatures (78-450 K) are reported for the first time and results are interpreted. Magnetic studies on Mn₂Mo₃O₈ in the temperature range, 10-350 K confirm that it is ferrimagnetic, with T_C = 39 K. Magnetic hysteresis and magnetization data at various fields and temperatures are presented. The Li-cyclability is investigated by galvanostatic cycling in the voltage range, 0.005-3.0 V vs. Li at 30 mA/g (0.08 C). LiYMo₃O₈ shows a total first-discharge capacity of 305 ±5 mAh/g whereas the first-charge capacity is only 180 mAh/g at RT. However, both values increased systematically with an increase in the cycle number and yielded a reversible capacity of 385 ±5 mAh/g at the end of 120th cycle. At 50 °C, the reversible capacity is 418 ±5 mAh/g at the 60th cycle. The coulombic efficiency ranges from 94% to 98%. The Li-cyclability behavior of Mn₂Mo₃O₈ is entirely different from that of LiYMo₃O₈. The total first-discharge and charge capacities are 710 ± 5 and 565 ±5 mAh/g, but drastic capacity-fading occurs during cycling. The reversible capacity at the end of 50th cycle is only 205 ±5 mAh/g. Plausible reaction mechanisms are proposed and discussed based on the galavanostatic cycling, cyclic voltammetry, ex situ XRD, ex situ TEM and impedance spectral data.     

Structure and electrochemical properties of nanocarbon-coated Li3V2(PO4)3 prepared by sol-gel method

A liquid-based sol-gel method was developed to synthesize nanocarbon-coated Li₃V₂(PO₄)₃. The products were characterized by XRD, SEM and electrochemical measurements. The results of Rietveld refinement analysis indicate that single-phase Li₃V₂(PO₄)₃ with monoclinic structure can be obtained in our experimental process. The discharge capacity of carbon-coated Li₃V₂(PO₄)₃ was 152.6 mAh/g at the 50th cycle under 1C rate, with 95.4% retention rate of initial capacity. A high discharge capacity of 184.1 mAh/g can be obtained under 0.12C rate, and a capacity of 140.0 mAh/g can still be held at 3C rate. The cyclic voltammetric measurements indicate that the electrode reaction reversibility is enhanced due to the carbon-coating. SEM images show that the reduced particle size and well-dispersed carbon-coating can be responsible for the good electrochemical performance obtained in our experiments.     

Properties of nano-crystalline LiMn2O4 thin films deposited by pulsed laser deposition

Properties of LiMn₂O₄ thin films deposited on polished stainless steel substrates at 400 °C and 200 mTorr of oxygen by pulsed laser deposition have been characterized by electrochemical measurements and physical analyses. The film was mainly composed of nano-crystals less than 100 nm. A maximum specific capacity of 141.9 mAh/g cycled between 3.0 and 4.5 V with a current density of 20 μAh/cm² has been achieved. The film exhibited an excellent cycling stability up to 500 cycles. The low charge-transfer resistance at high potentials as revealed by AC impedance resulted in high charge/discharge potential and more capacity. The effect of overdischarge was limited and Jahn-Teller effect was overcome to a significant extent in this nano-crystalline film. Ex situ XRD, Raman and XPS provided supporting evidence in the changes in structure, reactivity and cycling stability of nano-crystalline LiMn₂O₄ film cathodes under different charge/discharge states and cycling tests. SEM images also revealed the stability of the surface topography after a long-term cycling test.     

Hydrothermal synthesis of Li4Ti5O12 microsphere with high capacity as anode material for lithium ion batteries

Lithium titanate (Li₄Ti₅O₁₂) microsphere has been successfully synthesized by a hydrothermal method. X-ray diffraction (XRD) and scanning electron microscope (SEM) are used to characterize the structure and morphology of the prepared Li₄Ti₅O₁₂ crystallites. The results show that the as-synthesized powders exhibit outstanding rate capacities and excellent cycling performance. The first discharge capacity at 0.1 C is 172.5 mAh g⁻¹, which is close to the theoretical capacity of 175 mAh/g. After 50 cycles, the efficiency of the synthesized Li₄Ti₅O₁₂ still retains up to 92.8% at 0.1 C and 95.2% at 0.5 C of its initial value, which present a promising applications as anode materials for lithium ion batteries in hybrid and plug-in hybrid electric vehicles.     

Preparation and electrochemical performance of Li4Ti5O12/carbon/carbon nano-tubes for lithium ion battery

A Li₄Ti₅O₁₂/carbon/carbon nano-tubes (Li₄Ti₅O₁₂/C/CNTs) composite was synthesized by using a solid-state method. For comparison, a Li₄Ti₅O₁₂/carbon (Li₄Ti₅O₁₂/C) composite and a pristine Li₄Ti₅O₁₂ were also synthesized in the present study. The microstructure and morphology of the prepared samples are characterized by XRD and SEM. Electrochemical properties of the samples are evaluated by using galvanostatic discharge/charge tests and AC impedance spectroscopy. The results reveal that the Li₄Ti₅O₁₂/C/CNTs composite exhibits the best rate capability and cycling stability among the samples of Li₄Ti₅O₁₂, Li₄Ti₅O₁₂/C and Li₄Ti₅O₁₂/C/CNTs. At the charge-discharge rate of 0.5 C, 5.0 C and 10.0 C, its discharge capacities were 163 mAh/g, 148 mAh/g and 143 mAh/g, respectively. After 100 cycles at 5.0 C, it remained at 146 mAh/g.     

Synthesis and electrochemical performance of LiNi0.5Mn1.5O4 spinel compound

Spinel compound LiNi_0.5Mn_1.5O₄ was synthesized by a chemical wet method. Mn(NO₃)₂, Ni(NO₃)₂·6H₂O, NH₄HCO₃ and LiOH·H₂O were used as the starting materials. At first, Mn(NO₃)₂ and Ni(NO₃)₂·6H₂O reacted with NH₄HCO₃ to produce a precursor, then the precursor reacted with LiOH·H₂O to synthesize product LiNi_0.5Mn_1.5O₄. The product showed a single spinel phase under appropriate calcination conditions, and exhibited a high voltage plateau at about 4.6-4.8 V in the charge/discharge process. The LiNi_0.5Mn_1.5O₄ had a discharge specific capacity of 118 mAh/g at about 4.6 V and 126 mAh/g in total in the first cycle at a discharge current density of 2 mA/cm². After 50 cycles, the total discharge capacity was above 118 mAh/g.     

The structure and electrochemical performance of LiFeBO3 as a novel Li-battery cathode material

LiFeBO₃ cathode material has been synthesized successfully by solid-state reaction using Li₂CO₃, H₃BO₃ and FeC₂O₄·2H₂O as starting materials. The crystal structure has been determined by the X-ray diffraction. Electrochemical tests show that an initial discharge capacity of about 125.8 mAh/g can be obtained at the discharge current density of 5 mA/g. When the discharge current density is increased to 50 mA/g, the specific capacity of 88.6 mAh/g can still be held. In order to further improve the electrochemical properties, the carbon-coated LiFeBO₃, C-LiFeBO₃, are also prepared. The amount of carbon coated on LiFeBO₃ particles was determined to be around 5% by TG analysis. In comparison with the pure LiFeBO₃, a higher discharge capacity, 158.3 mAh/g at 5 mA/g and 122.9 mAh/g at 50 mA/g, was obtained for C-LiFeBO₃. Based on its low cost and reasonable electrochemical properties obtained in this work, LiFeBO₃ may be an attractive cathode for lithium-ion batteries.     

Electrochemical properties of carbon-coated CaWO4 versus Li

Carbon-coated CaWO₄ nano-crystalline phases have been synthesized by ambient temperature solution precipitation method, characterized by X-ray diffraction, SEM and thermogravimetry and their electrochemical properties were studied versus Li metal. Galvanostatic cycling at a current of 60 mA/g in the voltage range 0.005-3.0 V on the 5 wt.% C-coated CaWO₄ gave a reversible capacity of 230 ± 5 mAh/g corresponding to 2.5 mol of Li, which is almost stable from 20 to 50 cycles. Under the same conditions, the 10 wt.% C-coated CaWO₄ showed a capacity of 355 ± 5 mAh/g (3.8 mol of Li) during the initial cycles, but the capacity degraded at a rate of 1.6 mAh/g per cycle in the range 5-100 cycles. A good operating voltage range was found to be 0.005-3.0 V with average discharge and charge potentials being 0.6 and 1.3 V, respectively. Coulombic efficiency in all cases was 96-98%. Cyclic voltammograms compliment the galvanostatic results. Impedance spectral data on the 10 wt.% C-coated CaWO₄ at different voltages during the first and 20th discharge-charge cycle have been interpreted in terms of the variations in the bulk and charge-transfer resistances of the composite electrode. A reaction mechanism involving the formation/decomposition of the oxide bronze, ‘Li_xWO_y’ has been proposed to explain the electrochemical cycling.     

Synthesis of spherical LiMn2O4 cathode material by dynamic sintering of spray-dried precursors

Spherical LiMn₂O₄ particles were successfully synthesized by dynamically sintering spherical precursor powders, which were prepared by a slurry spray-drying method. The effect of the sintering process on the morphology of LiMn₂O₄ was studied. It was found that a one-step static sintering process combined with a spray-drying method could not be adopted to prepare spherical products. A two-step sintering procedure consisting of completely decomposing sprayed precursors at low temperature and further sintering at elevated temperature facilitated spherical particle formation. The dynamic sintering program enhanced the effect of the two-step sintering process in the formation of spherical LiMn₂O₄ powders. The LiMn₂O₄ powders prepared by the dynamic sintering process, after initially decomposing the spherical spray-dried precursor at 180 °C for 5 h and then sintering it at 700 °C for 8 h, were spherical and pure spinel. The as-prepared spherical material had a high tap density (ca. 1.6 g/cm³). Its specific capacity was about 117 mAh/g between 3.0 and 4.2 V at a rate of 0.2 C. The retention of capacity for this product was about 95% over 50 cycles. The rate capability test indicated that the retention of the discharge capacity at 4C rate was still 95.5% of its 0.2 rate capacity. All the results showed that the spherical LiMn₂O₄ product made by the dynamic sintering process had a good performance for lithium ion batteries. This novel method combining a dynamic sintering system and a spray-drying process is an effective synthesis method for the spherical cathode material in lithium ion batteries.     

A promising sol-gel route based on citric acid to synthesize Li3V2(PO4)3/carbon composite material for lithium ion batteries

Li₃V₂(PO₄)₃/carbon composite material was synthesized by a promising sol-gel route based on citric acid using V₂O₅ powder as a vanadium source. Citric acid acts not only as a chelating reagent but also as a carbon source, which enhance the conductivity of the composite material and hinder the growth of Li₃V₂(PO₄)₃ particles. The structure and morphology of the sample were characterized by TG, XRD and TEM measurements. XRD results reveal that Li₃V₂(PO₄)₃/carbon was successfully synthesized and has a monoclinic structure with space group P2₁/n. TEM images show Li₃V₂(PO₄)₃ particles are about 45 nm in diameter embeded in carbon networks. Galvanostatic charge/discharge and cyclic voltammetry measurements were used to study its electrochemical behaviors which indicate the reversibility of the lithium extraction/insertion processes. Li₃V₂(PO₄)₃/carbon performed in a voltage window (3.0-4.8 V) exhibits higher discharge capacity, better cycling stability and its discharge capacity maintains about 167.6 mAh/g at a current density of 28 mA/g after 50 cycles.     

Electrochemical properties of TiP2O7 and LiTi2(PO4)3 as anode material for lithium ion battery with aqueous solution electrolyte

Some polyanionic compounds, e.g. TiP₂O₇ and LiTi₂(PO₄)₃ with 3D framework structure were proposed to be used as anodes of lithium ion battery with aqueous electrolyte. The cyclic voltammetry properties TiP₂O₇ and LiTi₂(PO₄)₃ suggested that Li-ion de/intercalation reaction can occur without serious hydrogen evolution in 5 M LiNO₃ aqueous solution. The TiP₂O₇ and LiTi₂(PO₄)₃ give capacities of about 80 mAh/g between potentials of −0.50 V and 0 V (versus SHE) and 90 mAh/g between −0.65 V and −0.10 V (versus SHE), respectively. A test cell consisting of TiP₂O₇/5 M LiNO₃/LiMn₂O₄ delivers approximately 42 mAh/g (weight of cathode and anode) at average voltage of 1.40 V, and LiTi₂(PO₄)₃/5 M LiNO₃/LiMn₂O₄ delivers approximately 45 mAh/g at average voltage of 1.50 V. Both as-assembled cells suffered from short cycle life. The capacity fading may be related to deterioration of anode material.     

A delithiated LiNi0.65Co0.25Mn0.10O2 electrode material: A structural, magnetic and electrochemical study

A crystalline LiNi_0.65Co_0.25Mn_0.10O₂ electrode material was synthesized by the combustion method at 900 °C for 1 h. Rietveld refinement shows less than 3% of Li/Ni disorder in the structure. Lithium extraction involves only the Ni²⁺/Ni⁴⁺ redox couple while Co³⁺ and Mn⁴⁺ remain electrochemically inactive. No structural transition was detected during cycling in the whole composition range 0 < x < 1.0. Furthermore, the hexagonal cell volume changes by only 3% when all lithium was removed indicating a good mechanical stability of the studied compound. LiNi_0.65Co_0.25Mn_0.10O₂ has a discharge capacity of 150 mAh/g in the voltage range 2.5-4.5 V, but the best electrochemical performance was obtained with an upper cut-off potential of 4.3 V. Magnetic measurements reveal competing antiferromagnetic and ferromagnetic interactions - varying in strength as a function of lithium content - yielding a low temperature magnetically frustrated state. The evolution of the magnetic properties with lithium content confirms the preferential oxidation of Ni ions compared to Co³⁺ and Mn⁴⁺ during the delithiation process.     

Electrochemical characterization of amorphous LiFe(WO4)2 thin films as positive electrodes for rechargeable lithium batteries

Amorphous LiFe(WO₄)₂ thin films have been fabricated by radio-frequency (R.F.) sputtering deposition at room temperature. The as-deposited and electrochemically cycled thin films are, respectively, characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and X-ray photoelectron spectra techniques. An initial discharge capacity of 198 mAh/g in Li/LiFe(WO₄)₂ cells is obtained, and the electrochemical behavior is mostly preserved in the following cycling. These results identified the electrochemical reactivity of two redox couples, Fe³⁺/Fe²⁺ and W⁶⁺/W^x+ (x = 4 or 5). The kinetic parameters and chemical diffusion coefficients of Li intercalation/deintercalation are estimated by cyclic voltammetry and alternate-current (AC) impedance measurements. All-solid-state thin film lithium batteries with Li/LiPON/LiFe(WO₄)₂ layers are fabricated and show high capacity of 104 μAh/cm² μm in the first discharge. As-deposited LiFe(WO₄)₂ thin film is expected to be a promising positive electrode material for future rechargeable thin film batteries due to its large volumetric rate capacity, low-temperature fabrication and good electrode/electrolyte interface.