AlF<Subscript>3</Subscript> coating of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> for high-performance Li-ion batteries

AlF₃-coating is attempted to improve the performance of LiNi_0.5Mn_1.5O₄ cathode materials for Li-ion batteries. The prepared powders are characterized by scanning electron microscope, powder X-ray diffraction, charge/discharge, and impedance. The coated LiNi_0.5Mn_1.5O₄ samples show higher discharge capacity, better rate capability, and higher capacity retention than the uncoated samples. Among the coated samples, 1.0 mol% AlF₃-coated sample shows highest capacity after charge–discharged at 30 mA/g for 3 cycles, but 4.0 mol% coated sample exhibits the highest capacity and cycling stability when cycled at high rate of 150 and 300 mA/g. The 40th cycle discharge capacity at 300 mA/g current still remains 114.8 mAh/g for 4.0 mol% AlF₃-coated LiNi_0.5Mn_1.5O₄, while only 84.3 mAh/g for the uncoated sample.     

Low-temperature synthesis of Cu-doped Li<Subscript>1.2</Subscript>V<Subscript>3</Subscript>O<Subscript>8</Subscript> as cathode for reversible lithium storage

Li_{1 .2}V₃O₈ and Cu-doped Li_1.2V₃O₈ were prepared at a temperature as low as 300 °C by a sol-gel method. The structure, morphology, and electrochemical performance of the as-prepared samples were characterized by means of X-ray diffraction, scanning electron microscopy, electrochemical impedance spectroscopy, and the galvanostatic discharge–charge techniques. It is found that the Cu-doped Li_1.2V₃O₈ sample exhibits less capacity loss during repeated cycling than the undoped one. The Cu-doped Li_1.2V₃O₈ sample demonstrates the first discharge capacity of 275.9 mAh/g in the range of 3.8–1.7 V at a current rate of 30 mA/g and remains at a stable discharge capacity of 264 mAh/g within 30 cycles. Furthermore, the possible role that copper plays in enhancing the cycleability of Li_1.2V₃O₈ has also been elucidated.     

Effects of doping Al on the structure and electrochemical performances of Li[Li<Subscript>0.2</Subscript>Mn<Subscript>0.54</Subscript>Ni<Subscript>0.13</Subscript>Co<Subscript>0.13</Subscript>]O<Subscript>2</Subscript> cathode materials

The Li-rich cathode material Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ had been successfully synthesized by a carbonate coprecipitation method. The effects of substituting traces of Al element for different transitional metal elements on the crystal structure and surface morphology had been investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy. The results revealed that all the materials showed similar XRD patterns and surface morphology. It was demonstrated that LNCMAl1 exhibited the superior electrochemical performance. The discharge capacity was 265.2 mAh g^?1 at 0.1 C and still maintained a discharge capacity of 135.6 mAh g^?1 at 5.0 C. The capacity retention could still be 58.2 and 66.8% after 50 cycles at 1.0 and 2.0 C, respectively. Electrochemical impedance spectra results proved that the remarkably improved rate capability and cycling performance could be ascribed to the low charge transfer resistance and enhanced reaction kinetics.     

Modification research of LiAlO<Subscript>2</Subscript>-coated LiNi<Subscript>0.8</Subscript>Co<Subscript>0.1</Subscript>Mn<Subscript>0.1</Subscript>O<Subscript>2</Subscript> as a cathode material for lithium-ion battery

The LiNi_0.8Co_0.1Mn_0.1O₂ with LiAlO₂ coating was obtained by hydrolysis–hydrothermal method. The morphology of the composite was characterized by SEM, TEM, and EDS. The results showed that the LiAlO₂ layer was almost completely covered on the surface of particle, and the thickness of coating was about 8–12 nm. The LiAlO₂ coating suppressed side reaction between composite and electrolyte; thus, the electrochemical performance of the LiAlO₂-coated LiNi_0.8Co_0.1Mn_0.1O₂ was improved at 40 °C. The LiAlO₂-coated sample delivered a high discharge capacity of 181.2 mAh g^?1 (1 C) with 93.5% capacity retention after 100 cycles at room temperature and 87.4% capacity retention after 100 cycles at 40 °C. LiAlO₂-coated material exhibited an excellent cycling stability and thermal stability compared with the pristine material. These works will contribute to the battery structure optimization and design.     

Influence of cooling mode on the electrochemical properties of Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> anode materials for lithium-ion batteries

Li₄Ti₅O₁₂ (LTO) was synthesized with two different cooling methods by solid-state method, namely fast cooling and air cooling. The samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), galvanostatic charge–discharge test, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), respectively. XRD revealed that the basic LTO structure was not changed. FESEM images showed that fast cooling effectively reduced the particle sizes and the agglomeration of particles. Galvanostatic charge–discharge test showed that the air cooling sample exhibited a mediocre performance, having an initial discharge capacity of 136.3mAh?·?g^?1 at 0.5 C; however, the fast cooling sample demonstrated noticeable improvement in both of its discharge capacity and rate capability, with a high initial capacity value of 142.7 mAh?·?g^?1 at 0.5 C. CV measurements also revealed that fast cooling enhanced the reversibility of the LTO. EIS confirmed that fast cooling resulted in lower electrochemical polarization and a higher lithium-ion diffusion coefficient. Therefore, fast cooling have a great impact on discharge capacity, rate capability, and cycling performance of LTO anode materials for lithium-ion batteries.     

Lithium polyacrylate-coated LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode materials with excellent performance for lithium ion batteries

A novel facile approach to coat LiMn₂O₄ by lithium polyacrylate (PAALi) is demonstrated. The PAALi-coated LiMn₂O₄ (LMO@2%PAALi) and LiMn₂O₄ (LMO) are characterized by charge–discharge tests, X-ray diffraction (XRD), PAALi dissolving experiment, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), and inductively coupled plasma optical emission spectrometer (ICP-OES). XRD and FTIR analyses indicate that there are no clear differences between LMO@2%PAALi and LMO. PAALi dissolving experiment indicates that PAALi is indissolvable in LiPF₆-EC/DMC/EMC electrolyte. TEM results reveal that LiMn₂O₄ particles are coated by PAALi. ICP-OES results indicate that this stable PAALi coating can prevent the Mn ions dissolving from active LiMn₂O₄ materials and then the stability of LiMn₂O₄ crystals in electrolyte are greatly enhanced. These unique features ensure that LMO@2%PAALi possesses much better rate performance, higher discharge capacity, better cycling performance, and lower charge transfer resistance over LMO. The discharge capacity of LMO@2%PAALi at 0.2 C reaches up to 127.2 mAh g^?1 at room temperature.     

Effect of passivating Al<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films on MnO<Subscript>2</Subscript>/carbon nanotube composite lithium-ion battery anodes

MnO₂/carbon nanotube composite electrodes for Li-ion battery application were directly coated with ultrathin thicknesses of aluminum oxide film by atomic layer deposition (ALD). The non-reactive Al₂O₃ layer not only provides a stable film to protect the manganese oxide and carbon nanotubes from undesirable reaction with the electrolyte but also restrains the volume change strain of manganese oxide during cycling. The first cycle Coulombic efficiency of coated samples was increased to different extents depending on the coating thickness. In the following cycles, the coated electrodes denote high specific capacity, good capacity retention ability, and perfect rate charge/discharge performance.     

Influence of charge rate on the cycling degradation of LiFePO<Subscript>4</Subscript>/mesocarbon microbead batteries under low temperature

The lithium-ion batteries show extremely poor cycling performance at low temperature. The main degradation mechanism is not clear. To address the fading mechanism, the cycling degradation of commercial LiFePO₄/mesocarbon microbead (MCMB) batteries under various charge rate (1/10C, 1/3C, 1/2C, and 1C) at ?10 °C is systematically investigated using nondestructive tests combining with post-mortem analysis. The low-temperature charging under high charge rates of 1/3C, 1/2C, and 1C results in severe lithium plating, which leads to extremely serious capacity loss. In contrast, no lithium plating occurred under low charge rate of 1/10C. The lithium plating on the anode surface leads to consumption of active lithium ions and electrolyte, which causes the capacity decay and increases ohmic resistance (R _b) with cycling number under high charge rates. The lithium plating on the anode surface is partially reversible, which brings about the capacity recovery of batteries after 80 cycles at 25 °C. The above results are proved by the followed post-mortem measurements. The evolution of the surface morphologies of MCMB electrodes upon cycling shows that a layer composed of rod-like lithium is formed on the anode surface.     

Improvement of cycling and thermal stability of LiNi<Subscript>0.8</Subscript>Mn<Subscript>0.1</Subscript>Co<Subscript>0.1</Subscript>O<Subscript>2</Subscript> cathode material by secondly treating process

(Ni_0.8Mn_0.1Co_0.1)(OH)₂ and Co(OH)₂ secondly treated by LiNi_0.8Mn_0.1Co_0.1O₂ have been prepared via co-precipitation and high-temperature solid-state reaction. The residual lithium contents, XRD Rietveld refinement, XPS, TG-DSC, and electrochemical measurements are carried out. After secondly treating process, residual lithium contents decrease drastically, and occupancy of Ni in 3a site is much lower and Li/Ni disorder decreases. The discharge capacity is 193.1, 189.7, and 182 mAh g^?1 at 0.1 C rate, respectively, for LiNi_0.8Mn_0.1Co_0.1O₂-AP, -NT, and -CT electrodes between 3.0 and 4.2 V in pouch cell. The capacity retention has been greatly improved during gradual capacity fading of cycling at 1 C rate. The noticeably improved thermal stability of the samples after being treated can also be observed.     

Polyaspartic-acid-pyrolysis route for the synthesis of nanocrystalline LiCo<Subscript>0.15</Subscript>Mn<Subscript>1.85</Subscript>O<Subscript>4</Subscript> powder for Li-ion batteries

Nanocrystalline cubic spinel LiCo_0.15Mn_1.85O₄ powder was prepared by a novel method based on in situ polymerization of aspartic acid along with metal salts. Thermal study shows that the complete crystallization and/or formation of the compound is at 358 °C. The structural property of the synthesized material was characterized by X-ray diffraction studies. The X-ray diffractogram reveals the single-phase formation of the product. Scanning electron microscope study shows that the average grain size of the powder is less than 1 μm. To assess the electrochemical performance of the synthesized cathode material, the C/LiCo_0.15Mn_1.85O₄ cell with 1 M LiPF₆ in 1:1 (v/v) mixture of ethylene carbonate and dimethyl carbonate as the electrolyte was assembled, and the charge and discharge studies were made in between 3.0 and 4.8 V at a constant current density of 0.1 mAcm⁻². It shows that capacity loss is only 2% even after the 50th cycle. As this preparation method is simple and particularly suitable for preparation of highly homogeneous mixed metal oxides for Li-ion batteries.     

LiFePO<Subscript>4</Subscript>/C with high capacity synthesized by carbothermal reduction method

The olivine-type LiFePO₄/C cathode materials were prepared via carbothermal reduction method using cheap Fe₂O₃ as raw material and different contents of glucose as the reducing agent and carbon source. Their structural and morphological properties were investigated by X-ray diffraction, scanning electron microscope, transmission electron microscope, and particle size distribution analysis. The results demonstrated that when the content of the carbon precursor of glucose was 16 wt.%, the synthesized powder had good crystalline and exhibited homogeneous and narrow particle size distribution. Even and thin coating carbon film was formed on the surface of LiFePO₄ particles during the pyrolysis of glucose, resulting in the enhancement of the electronic conductivity. Electrochemical tests showed that the discharge capacity first increased and then decreased with the increase of glucose content. The optimal sample synthesized using 16 wt.% glucose as carbon source exhibited the highest discharge capacity of 142 mAh g⁻¹ at 0.1C rate with the capacity retention rate of 90.4% and 118 mAh g⁻¹ at 0.5C rate.     

Vinyl ethylene carbonate as an electrolyte additive for high-voltage LiNi<Subscript>0.4</Subscript>Mn<Subscript>0.4</Subscript>Co<Subscript>0.2</Subscript>O<Subscript>2</Subscript>/graphite Li-ion batteries

Vinyl ethylene carbonate (VEC) is investigated as an electrolyte additive to improve the electrochemical performance of LiNi_0.4Mn_0.4Co_0.2O₂/graphite lithium-ion battery at higher voltage operation (3.0–4.5 V) than the conventional voltage (3.0–4.25 V). In the voltage range of 3.0–4.5 V, it is shown that the performances of the cells with VEC-containing electrolyte are greatly improved than the cells without additive. With 2.0 wt.% VEC addition in the electrolyte, the capacity retention of the cell is increased from 62.5 to 74.5 % after 300 cycles. The effects of VEC on the cell performance are investigated by cyclic voltammetry(CV), electrochemical impedance spectroscopy(EIS), x-ray powder diffraction (XRD), energy dispersive x-ray spectrometry (EDS), scanning electron microscopy (SEM), and attenuated total reflectance-Fourier transform infrared (ATR-FTIR). The results show that the films electrochemically formed on both anode and cathode, derived from the in situ decomposition of VEC at the initial charge–discharge cycles, are the main reasons for the improved cell performance.     

Thermoeletrochemical study on LiNi<Subscript>0.8</Subscript>Co<Subscript>0.1</Subscript>Mn<Subscript>0.1</Subscript>O<Subscript>2</Subscript> with in situ modification of Li<Subscript>2</Subscript>ZrO<Subscript>3</Subscript>

To improve the electrochemical performance of Nickel-rich cathode material LiNi_0.8Co_0.1Mn_0.1O₂, an in situ coating technique with Li₂ZrO₃ is successfully applied through wet chemical method, and the thermoelectrochemical properties of the coated material at different ambient temperatures and charge-discharge rates are investigated by electrochemical-calorimetric method. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests demonstrate that the Li₂ZrO₃ coating decreases the electrode polarizatoin and reduces the charge transfer resistance of the material during cycling. Moreover, it is found that with the ambient temperatures and charge-discharge rates increase, the specific capacity decreases, the amount of heat increases, and the enthalpy change (ΔH) increases. The specific capacity of the cells at 30 °C are 203.8, 197.4, 184.0, and 174.5 mAh g^?1 at 0.2, 0.5, 1.0, and 2.0 C, respectively. Under the same rate (2.0 C), the amounts of heat of the cells are 381.64, 645.32, and 710.34 mJ at 30, 40, and 50 °C. These results indicate that Li₂ZrO₃ coating plays an important role to enhance the electrochemical performance of LiNi_0.8Co_0.1Mn_0.1O₂ and reveal that choosing suitable temperature and current is critical for solving battery safety problem.     

Advanced LiTi<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C anode by incorporation of carbon nanotubes for aqueous lithium-ion batteries

Inferior rate capability is a big challenge for LiTi₂(PO₄)₃ anode for aqueous lithium-ion batteries. Herein, to address such issue, we synthesized a high-performance LiTi₂(PO₄)₃/carbon/carbon nanotube (LTP/C/CNT) composite by virtue of high-quality carbon coating and incorporation of good conductive network. The as-prepared LTP/C/CNT composite exhibits excellent rate performance with discharge capacity of 80.1 and 59.1 mAh g^?1 at 10 C and 20 C (based on the mass of anode, 1 C = 150 mA g^?1), much larger than that of the LTP/C composite (53.4 mAh g^?1 at 10 C, and 31.7 mAh g^?1 at 20 C). LTP/C/CNT also demonstrates outstanding cycling stability with capacity retention of 83.3 % after 1000 cycles at 5 C, superior to LTP/C without incorporation of CNTs (60.1 %). As verified, the excellent electrochemical performance of the LTP/C/CNT composite is attributed to the enhanced electrical conductivity, rapid charge transfer, and Li-ion diffusion because of the incorporation of CNTs.     

Synthesis and characterization of pristine Li<Subscript>2</Subscript>MnSiO<Subscript>4</Subscript> and Li<Subscript>2</Subscript>MnSiO<Subscript>4</Subscript>/C cathode materials for lithium ion batteries

The cathode materials, pristine Li₂MnSiO₄ and carbon-coated Li₂MnSiO₄ (Li₂MnSiO₄/C), were synthesized by the sol–gel method. Power X-ray diffraction and scanning electron microscopy analyses show that the presence of carbon during synthesis can weaken the formation of impurities in the final product and decrease the particle size of the final product. The effects of carbon coating on electrochemical characteristics were investigated by galvanostatic cycling test and electrochemical impedance spectroscopy. The galvanostatic cycling test results indicate that Li₂MnSiO₄/C cathode exhibits better electrochemical performance with an initial discharge capacity of 134.4 mAh g⁻¹ and a capacity retention of 63.9 mAh g⁻¹ after 20 cycles. Electrochemical impedance analyses confirm that carbon coating can increase electronic conductivity, which results in good electrochemical performance of Li₂MnSiO₄/C cathode. The two semicircles and the large arc obtained in this study can be attributed to the migration of lithium ions through the solid electrolyte interphase films, the electronic properties of the material, and the charge transfer step, respectively.     

Low content Ni and Cr co-doped LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> with enhanced capacity retention

Nanoparticles of the pure and Ni–Cr co-doped lithium manganese oxides Li[Ni_xCr_yMn_2-x-y]O₄ (x = y = 0.01–0.05) have been synthesized by sol–gel method using citric acid as a chelating agent. The effect of low-content doping was noted reflecting the faster ionic movement in the cathode material. The phase structure and morphology of the materials are characterized by XRD, FTIR, SEM and TEM. Electrochemical and impedance measurements established that low-content Ni–Cr substitution substantially improves the structural stability and high rate cycling performance of LiMn₂O₄. Among all the investigated compositions, LiNi_0.01Cr_0.01Mn_1.98O₄ demonstrated the best electrochemical performance. At a substantially high current rate of 5 C, 82% of the initial discharge capacity at 0.1 C is retained. Remarkably, after deep cycling at high rates, a discharge capacity of 104 mAhg^?1 is resumed upon reducing the current rate to 0.1 C which is 91% of the specific capacity in the first cycle.     

Synthesis and electrochemical performance of carbon-coated LiCoBO<Subscript>3</Subscript> as cathode materials for lithium-ion batteries

Carbon-coated LiCoBO₃ (LiCoBO₃/C) is prepared by sol-gel method and polyethylene glycol 6000 (PEG-6000) is chosen as carbon source. The LiCoBO₃/C sample exhibits an initial discharge capacity of 76.7 mAh g^?1 at 0.1 C, and it can deliver a discharge capacity of 65.9 mAh g^?1 after 50 cycles, while the LiCoBO₃ sample only presents a first discharge capacity of 34.3 and 16.8 mAh g^?1 at the 50th cycle, LiCoBO₃/C sample shows better cycling performance than that of LiCoBO₃. The improved electrochemical properties could be mainly ascribed to the conductive carbon network and the reduced particle size of the LiCoBO₃ powders. Electrochemical impedance spectroscopy (EIS) results confirm that carbon coating decreases the charge transfer resistance and improve the electrochemical reaction kinetics.     

Cells studies on PEO/PEG/NaClO<Subscript>3</Subscript> thin-film electrolyte system based on composite V<Subscript>2</Subscript>O<Subscript>5</Subscript> electrode

The thin-film solid polymer electrolyte based on polyethylene oxide (PEO) with sodium chlorite (NaClO₃) has been prepared by a solution-cast technique. The electrolyte was characterized by X-ray diffraction (XRD), infrared (IR), cyclic voltammetry, alternating current conductivity, and Wagner’s polarization studies. The complexation of NaClO₃ with PEO was confirmed through the XRD and IR studies. The transference number measurement has shown that the ion transport is predominant over electrons in the polymer electrolytes (t _ions ≈ 0.94). The conductivity enhancement was observed in the case of the PEO/NaClO₃ system with the addition of plasticizers (low-molecular-weight polyethylene glycol, organic solvents propylene carbonate and dimethyl formamide. Cyclic voltammetry analysis showed the stability and redox character of the electrolyte and electrode. Finally, polymer electrolyte systems were examined by electrochemical cell studies using V₂O₅ and composite V₂O₅ cathode at temperature of 35 °C. Overall, the plasticized electrolyte shows a better electrochemical performance, and a higher discharge capacity was observed in composite V₂O₅-based cells over V₂O₅-based cells.     

Influence of co-precipitation temperature on microstructure and electrochemical properties of Li[Li<Subscript>0.2</Subscript>Mn<Subscript>0.54</Subscript>Ni<Subscript>0.13</Subscript>Co<Subscript>0.13</Subscript>]O<Subscript>2</Subscript> cathode materials for lithium ion batteries

The layered Li-rich Mn-based cathode materials Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ were prepared by using co-precipitation technique at different temperatures, and their crystal microstructure and particle morphology were observed and analyzed by XRD and SEM. The electrochemical properties of these samples were investigated by using charge-discharge tests, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV), respectively. The results indicated that all samples are of high purity. When the precursors were co-precipitated at 50 °C, their cathode materials have the most uniform and full particles and exhibit the highest initial discharge capacity (289.4 mAh/g at 0.1C), the best cycle stability (capacity retention rate of 91.2 % after 100 cycles at 0.5C), and the best rate performance. The EIS results show that the lower charge transfer resistance of 50 °C sample is responsible for its superior discharge capacity and rate performance.     

ZnO-coated LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode material for lithium-ion batteries synthesized by a combustion method

ZnO-coated LiMn₂O₄ cathode materials were prepared by a combustion method using glucose as fuel. The phase structures, size of particles, morphology, and electrochemical performance of pristine and ZnO-coated LiMn₂O₄ powders are studied in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), galvanostatic charge-discharge test, and X-ray photoelectron spectroscopy (XPS). XRD patterns indicated that surface-modified ZnO have no obvious effect on the bulk structure of the LiMn₂O₄. TEM and XPS proved ZnO formation on the surface of the LiMn₂O₄ particles. Galvanostatic charge/discharge test and rate performance showed that the ZnO coating could improve the capacity and cycling performance of LiMn₂O₄. The 2 wt% ZnO-coated LiMn₂O₄ sample exhibited an initial discharge capacity of 112.8 mAh g^?1 with a capacity retention of 84.1 % after 500 cycles at 0.5 C. Besides, a good rate capability at different current densities from 0.5 to 5.0 C can be acquired. CV and EIS measurements showed that the ZnO coating effectively reduced the impacts of polarization and charge transfer resistance upon cycling.