Expanding performance limit of lithium-ion batteries simply by mixing Al(OH)3 powder with LiCoO2

Mixing a small amount of Al(OH)₃ powder with a LiCoO₂ cathode material is demonstrated to improve markedly the cycle performance and thermal stability of commercial grade LiCoO₂/graphite lithium-ion batteries. Al(OH)₃-mixed LiCoO₂/graphite prismatic cells exhibit excellent capacity retention as high as 95% after 400 cycles with negligible polarization build-up. Moreover, the thermal stability of the cells is greatly improved by Al(OH)₃ mixing, which is confirmed by higher residual and recovery capacity ratios after storage at 90 °C compared with a pristine cell. The beneficial effects of Al(OH)₃ are found to be related mainly to an improvement of the cathode side, which is ascribed to reduced unwanted side-reactions with the electrolyte.     

Enhanced electrochemical properties of LiFePO4 cathode for Li-ion batteries with amorphous NiP coating

Here we show that the intrinsic low electrical conductivity of LiFePO₄ which seriously hinders the application of LiFePO₄ for Li-ion batteries is overcome with conductive metallic NiP nano-coating. High resolution transmission electron microscopy image reveals that the NiP coating is a nanoscale amorphous layer, which was deposited on the LiFePO₄ particles to form a so-called core/shell structure via electroless plating at room temperature. The electrochemical performances of NiP coated LiFePO₄ show that both of the rate performance and cycleability of LiFePO₄ against graphite anode are improved by the NiP coating. Analysis of electrochemical impedance spectra of the LiFePO₄/graphite cells demonstrates that the NiP coating decreases both of the surface film resistance and charge transfer resistance. The dissolution of Fe from LiFePO₄ in the LiPF₆ based electrolyte is remarkably suppressed by the protective NiP coating.     

Effects of ZnO coating on electrochemical performance and thermal stability of LiCoO2 as cathode material for lithium-ion batteries

ZnO-coated LiCoO₂ particles are prepared by plasma-enhanced chemical vapour deposition (PE-CVD) in a coating range from 0.08 to 0.49 wt.%, and examined using field emission-scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and atomic absorption spectroscopy (AAS), with particular focus on surface characteristics. From charge-discharge cycling tests in the range of 3.0–4.5 V, the ZnO coating has little effect on the discharge capacity in the first few cycles, but the coating effectively improves the capacity retention after prolonged cycling. In the experimental range studied, the optimum amount of ZnO coating which maximizes the capacity retention is found to be 0.21 wt.%. An excessive amount of ZnO coating causes a decrease in both cyclic performance and thermal stability. The possible reasons for enhanced cycleability and thermal stability afforded by the ZnO coating are discussed from the viewpoint of the surface morphology of the bare and coated LiCoO₂ particles and their impedance spectra.     

Preparation and electrochemical investigation of Li2CoPO4F cathode material for lithium-ion batteries

In this paper, we report the electrochemical characteristics of a novel cathode material, Li₂CoPO₄F, prepared by solid-state reactions. The solid-state reaction mechanism involved in synthesizing the Li₂CoPO₄F also is analyzed in this paper. When cycled between 2.0 V and 5.0 V during cyclic voltammetry measurements, the Li₂CoPO₄F samples present one, fully reversible anodic reaction at 4.81 V. When cycled between 2.0 V and 5.5 V, peaks occurring at 4.81 V and 5.12 V in the first anodic scan evolved to one broad oxidative, mound-like pattern in subsequent cycles. Correspondingly, the X-ray diffraction (XRD) pattern of the Li₂CoPO₄F electrode discharged from 5.5 V to 2.0 V is slightly different from the patterns exhibited by a fresh sample and the sample discharged from 5.0 V to 2.0 V. This difference may correspond to a structural relaxation that appears above 5 V. In the constant current cycling measurements, the Li₂CoPO₄F samples exhibited a capacity as high as 109 mAh g⁻¹ and maintained a good cyclability between 2.0 V and 5.5 V vs. Li/Li⁺. XRD measurements confirmed that the discharged state is Li₂CoPO₄F. Combining these XRD results and electrochemical data proved that up to 1 mol Li⁺ is extractable when charged to 5.5 V.     

Synthesis and electrochemical performance of doped LiCoO2 materials

Layered intercalation compounds LiM_0.02Co_0.98O₂ (M = Mo⁶⁺, V⁵⁺, Zr⁴⁺) have been prepared using a simple solid-state method. Morphological and structural characterization of the synthesized powders is reported along with their electrochemical performance when used as the active material in a lithium half-cell. Synchrotron X-ray diffraction patterns suggest a single phase HT-LiCoO₂ that is isostructural to α-NaFeO₂ cannot be formed by aliovalent doping with Mo, V, and Zr. Scanning electron images show that particles are well-crystallized with a size distribution in the range of 1–5 μm. Charge–discharge cycling of the cells indicated first cycle irreversible capacity loss in order of increasing magnitude was Zr (15 mAh g⁻¹), Mo (22 mAh g⁻¹), and V (45 mAh g⁻¹). Prolonged cycling the Mo-doped cell produced the best performance of all dopants with a stable reversible capacity of 120 mAh g⁻¹ after 30 cycles, but was inferior to that of pure LiCoO₂.     

A novel and efficient water-based composite binder for LiCoO2 cathodes in lithium-ion batteries

The dispersion, adhesion strength, electrical, and electrochemical properties of LiCoO₂ cathodes in lithium-ion batteries with the addition of a new composite binder composed of two acrylic emulsions, poly(butyl acrylate)-based (PBA) and polyacrylonitrile-based (PA) latex in a ratio of 3:7, were evaluated. PBA binder has a low-glass transition temperature of 10 °C, which can improve the flexibility of the electrode. This new composite binder has a very good binding ability as same as the typical organic solvent-based binder, poly(vinylidene fluoride). The dispersions of the water-based cathode slurries with the composite binder were measured by analyzing the viscosity and sedimentation behaviors. The results show that the new composite binder can well disperse the LiCoO₂. Moreover, using the new composite binder could greatly improve the rate capabilities and the cycle stability of water-based LiCoO₂ cathodes.     

A new low-temperature synthesis and electrochemical properties of LiV3O8 hydrate as cathode material for lithium-ion batteries

LiV₃O₈, synthesized from V₂O₅ and LiOH, by heating of a suspension of V₂O₅ in a LiOH solution at a low-temperature (100-200 °C), exhibits a high discharge capacity and excellent cyclic stability at a high current density as a cathode material of lithium-ion battery. The charge-discharge curve shows a maximum discharge capacity of 228.6 mAh g⁻¹ at a current density of 150 mA g⁻¹ (0.5 C rate) and the 100 cycles discharge capacity remains 215 mAh g⁻¹. X-ray diffraction indicates the low degree of crystallinity and expanding of inter-plane distance of the LiV₃O₈ phase, and scanning electronic microscopy reveals the formation of nano-domain structures in the products, which account for the enhanced electrochemical performance. In contrast, the LiV₃O₈ phase formed at a higher temperature (300 °C) consists of well-developed crystal phases, and coherently, results in a distinct reduction of discharge capacity with cycle numbers. Thus, an enhanced electrochemical performance has been achieved for LiV₃O₈ by the soft chemical method via a low-temperature heating process.     

Synthesis and electrochemical performance of Li2CoSiO4 as cathode material for lithium ion batteries

Li₂CoSiO₄ has been prepared successfully by a solution route or hydrothermal reaction for the first time, and its electrochemical performance has been investigated primarily. Reversible extraction and insertion of lithium from and into Li₂CoSiO₄ at 4.1 V versus lithium have shown that this material is a potential candidate for the cathode in lithium ion batteries. At this stage reversible electrochemical extraction was limited to 0.46 lithium per formula unit for the Li₂CoSiO₄/C composite materials, with a charge capacity of 234 mAh g⁻¹ and a discharge capacity of 75 mAh g⁻¹.     

Dual active material composite cathode structures for Li-ion batteries

The efficacy of composite Li-ion battery cathodes made by mixing active materials that possessed either high-rate capability or high specific energy was examined. The cathode structures studied contained carbon-coated LiFePO₄ and either Li[Li_0.17Mn_0.58Ni_0.25]O₂ or LiCoO₂. These active materials were arranged using three different electrode geometries: fully intermixed, fully separated, or layered. Discharge rate studies, cycle-life evaluation, and electrochemical impedance spectroscopy studies were conducted using coin cell test structures containing Li-metal anodes. Results indicated that electrode configuration was correlated to rate capability and degree of polarization if there was a large differential between the rate capabilities of the two active material species.     

Characterization of LiCoO2 coated Li1.05Ni0.35Co0.25Mn0.4O2 cathode material for lithium secondary cells

In this study, nano-crystalline LiCoO₂ was coated onto the surface of Li_1.05Ni_0.35Co_0.25Mn_0.4O₂ powders via sol–gel method. The influence of the coating on the electrochemical behavior of Li_1.05Ni_0.35Co_0.25Mn_0.4O₂ is discussed. The surface morphology was characterized by transmission electron microscopy (TEM). Nano-crystallized LiCoO₂ was clearly observed on the surfaces of Li_1.05Ni_0.35Co_0.25Mn_0.4O₂. The phase and structural changes of the cathode materials before and after coating were revealed by X-ray diffraction spectroscopy (XRD). It was found that LiCoO₂ coated Li_1.05Ni_0.35Co_0.25Mn_0.4O₂ cathode material exhibited distinct surface morphology and lattice constants. Cyclic voltammetry (2.8–4.6 V versus Li/Li⁺) shows that the characteristic voltage transitions on cycling exhibited by the uncoated material are suppressed by the 7 wt.% LiCoO₂ coating. This behavior implies that LiCoO₂ inhibits structural change of Li_1.05Ni_0.35Co_0.25Mn_0.4O₂ or reaction with the electrolyte on cycling. In addition, the LiCoO₂ coating on Li_1.05Ni_0.35Co_0.25Mn_0.4O₂ significantly improves the rate capability over the range 0.1–4.0C. Comparative data for the coated and uncoated materials are presented and discussed.     

Thermal stability of FeF3 cathode for Li-ion batteries

The thermal stability of a FeF₃ cathode was quantitatively studied by differential scanning calorimetry (DSC). The cycled electrode without electrolyte was examined and found to become more thermally stable after Li-ion insertion. On the other hand, mixtures of cycled electrodes and electrolyte were investigated by changing the ratio of cycled electrode to electrolyte. The thermal decomposition of the electrolyte was mainly responsible for the exothermic heat for the discharged electrode and electrolyte combination. Although a reaction between the active materials of the electrode and electrolyte was observed for the mixture of the charged electrode and electrolyte, the exothermic heats were small. In contrast to lithium transition-metal oxide cathodes for lithium-ion batteries, the exothermic heat was suppressed by the FeF₃ electrode. Therefore, FeF₃ as a cathode for Li-ion batteries shows more thermal stability at elevated temperatures.     

Characterization of two lithiation reactions starting with an amorphous FePO4 precursor

LiFePO₄ was prepared using two synthetic routes which involved the precipitation and lithiation of an amorphous FePO₄ precursor followed by a thermal treatment. Both hydrated and dehydrated FePO₄ were used. The XRD patterns confirm the amorphous nature of both the precipitated and the lithiated product, while a crystalline LiFePO₄ product is obtained after thermal treatment. Mössbauer spectroscopy was used to analyse the oxidation state of iron during various stages of the reaction. The Mössbauer data demonstrates a large amount of Fe³⁺ ions in the lithiated samples which suggest that the lithiation reaction does not go to completion. Therefore, the formation of LiFePO₄ may be in part associated with the thermal treatment and not the lithiation step.     

Li2MnSiO4 as a potential Li-battery cathode material

Recently we synthesized and preliminary characterized a new material for potential use in Li-battery cathodes: Li₂MnSiO₄. Although its theoretical capacity is about 330 mAh g⁻¹, the actual measurements showed a much smaller value (about 120 mAh g⁻¹). One of the reasons for the poor performance could be the poor electronic conductivity (<10⁻¹⁴ S cm⁻¹ at RT) causing a huge polarization during charge–discharge. However, in the present paper we show that reducing the particle size down to the range of 20–50 nm and additional particle embedment into a carbon phase does not significantly improve the electrochemistry of Li₂MnSiO₄. Observations of structural changes during the first charge shows a complete loss of peaks when reaching the nominal composition of ca. Li₁MnSiO₄. The peaks are not recovered during subsequent cycling. It is supposed that extraction of Li causes significant structural changes so that the resulting material is only able to reversibly exchange a limited amount of Li.     

Effects of TiO2 coating on high-temperature cycle performance of LiFePO4-based lithium-ion batteries

LiFePO₄ particles were coated with TiO₂ (molar ratio = 3%) via a sol–gel process, and the effects of the coating on cycle performance of LiFePO₄ cathode at 55 °C against either a Li or a C (mesocarbon microbead) anode were investigated. It was found that, while the coating reduces capacity fading of the LiFePO₄/Li cell, it imposes a deteriorating effect on the LiFePO₄/C cell. Analyses on cell impedance and electrode surface morphology and composition showed that the oxide coating reduced Fe dissolution from the LiFePO₄ cathode and hence alleviated the impedance increase associated with the erosion process. This leads to reduced capacity fading as observed for the LiFePO₄/Li cell. However, the oxide coating itself was eroded upon cycling, and the dissolved Ti ions were subsequently reduced at the anode surface. Ti deposit on the C anode was found to be more active than Fe in catalyzing the formation of the solid-electrolyte interphase (SEI) layer, causing accelerated capacity decay for the LiFePO₄/C cell. The results point out the importance of evaluating the effect of cathode coating material on the anode side, which has generally been overlooked in the past studies.     

Effects of supersonic treatment on the electrochemical properties and crystal structure of LiMn1.5Ni0.5O4 as a cathode material for Li ion batteries

The electrochemical properties and crystal structure of LiMn_1.5Ni_0.5O₄ treated with supersonic waves in an aqueous Ni-containing solution were investigated by performing charge-discharge tests, inductively coupled plasma (ICP) analysis, scanning electron microscopy (SEM), iodometry, X-ray diffraction (XRD), powder neutron diffraction and synchrotron powder XRD. The charge-discharge curve of LiMn_1.5Ni_0.5O₄ versus Li/Li⁺ has plateaus at 4.1 and 4.7 V. The 4.1 V versus Li/Li⁺ plateau due to the oxidation of Mn^3+/4+ was reduced by the supersonic treatment. During the charge-discharge cycling test at 25 °C, the supersonic treatment increased the discharge capacity of the 50th cycle. Rietveld analysis of the neutron diffraction patterns revealed that the Ni occupancy of the 4b site in LiMn_1.5Mn_0.5O₄, which is mainly occupied by Ni, was increased by the supersonic treatment. This result suggests that Ni²⁺ is partially substituted for Mn^3+/4+ during the supersonic treatment.     

Preparation of LiCoPO4/C nanocomposite cathode of lithium batteries with high rate performance

LiCoPO₄/C nanocomposites could be successfully prepared by a combination of spray pyrolysis and wet ball-milling followed by heat treatment. X-ray diffraction analysis confirmed that the LiCoPO₄/C nanocomposites were well crystallized in an orthorhombic structure with Pmna space group. Scanning electron microscopy and transmission electron microscopy with equipped energy dispersive spectroscopy verified that the LiCoPO₄/C nanocomposites were the agglomerates of LiCoPO₄ primary particles with a geometric mean diameter of 87 nm, and the carbon was well distributed on the surface of the agglomerates. The LiCoPO₄/C nanocomposites were used as cathode active materials for lithium batteries, and the electrochemical tests were carried out for the cell Li|1 M LiPF₆ in EC:DMC = 1:1|LiCoPO₄/C at various charge-discharge rates. The cells delivered first discharge capacities of 142 and 109 mAh g⁻¹ at 0.05 and 20 C, respectively. Furthermore, the discharge capacity after 40 cycles corresponded to 87% of initial one at 0.1 C rate. The excellent rate capability of the cells is mainly due to the well distributed carbon on the LiCoPO₄ agglomerates, and a much smaller lithium ion diffusion distance in the electrode.     

Synthesis and characterization of Nd doped LiMn2O4 cathode for Li-ion rechargeable batteries

Spinel powders of LiMn_1.99Nd_0.01O₄ have been synthesized by chemical synthesis route to prepare cathodes for Li-ion coin cells. The structural and electrochemical properties of these cathodes were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, cyclic voltammetry, and charge-discharge studies. The cyclic voltammetry of the cathodes revealed the reversible nature of Li-ion intercalation and deintercalation in the electrochemical cell. The charge-discharge characteristics for LiMn_1.99Nd_0.01O₄ cathode materials were obtained in 3.4–4.3 V voltage range and the initial discharge capacity of this material were found to be about 149 mAh g⁻¹. The coin cells were tested for up to 25 charge-discharge cycles. The results show that by doping with small concentration of rare-earth element Nd, the capacity fading is considerably reduced as compared to the pure LiMn₂O₄ cathodes, making it suitable for Li-ion battery applications.     

A novel sol-gel method based on FePO4·2H2O to synthesize submicrometer structured LiFePO4/C cathode material

Carbon coated LiFePO₄/C cathode material is synthesized with a novel sol-gel method, using cheap FePO₄·2H₂O as both iron and phosphorus sources and oxalic acid (H₂C₂O₄·2H₂O) as both complexant and reductant. In H₂C₂O₄ solution, FePO₄·2H₂O is very simple to form transparent sols without controlling the pH value. Pure submicrometer structured LiFePO₄ crystal is obtained with a particle size ranging from 100 to 500 nm, which is also uniformly coated with a carbon layer, about 2.6 nm in thickness. The as-synthesized LiFePO₄/C sample exhibits high initial discharge capacity 160.5 mAh g⁻¹ at 0.1 C rate, with a capacity retention of 98.7% after 50th cycle. The material also shows good high-rate discharge performances, about 106 mAh g⁻¹ at 10 C rate. The improved electrochemical properties of as-synthesized LiFePO₄/C are ascribed to its submicrometer scale particles and low electrochemical impedance. The sol-gel method may be of great interest in the practical application of LiFePO₄/C cathode material.     

Surfactant based sol–gel approach to nanostructured LiFePO4 for high rate Li-ion batteries

Porous nanostructured LiFePO₄ powder with a narrow particle size distribution (100–300 nm) for high rate lithium-ion battery cathode application was obtained using an ethanol based sol–gel route employing lauric acid as a surfactant. The synthesized LiFePO₄ powders comprised of agglomerates of crystallites <65 nm in diameter exhibiting a specific surface area ranging from 8 m² g⁻¹ to 36 m² g⁻¹ depending on the absence or presence of the surfactant. The LiFePO₄ obtained using lauric acid resulted in a specific capacity of 123 mAh g⁻¹ and 157 mAh g⁻¹ at discharge rates of 10C and 1C with less than 0.08% fade per cycle, respectively. Structural and microstructural characterization were performed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) with energy dispersive X-ray (EDX) analysis while electronic conductivity and specific surface area were determined using four-point probe and N₂ adsorption techniques.     

Electrochemical performance of LiCoO2 cathodes by surface modification using lanthanum aluminum garnet

LiCoO₂ particles were coated with various wt.% of lanthanum aluminum garnets (3LaAlO₃:Al₂O₃) 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 3LaAlO₃:Al₂O₃ compound and the in situ sol–gel process synthesized 3LaAlO₃:Al₂O₃-coated LiCoO₂ was a single-phase hexagonal α-NaFeO₂-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 3LaAlO₃:Al₂O₃, which had an average thickness of 40 nm. Galvanostatic cycling studies demonstrated that the 1.0 wt.% 3LaAlO₃:Al₂O₃-coated LiCoO₂ cathode showed excellent cycle stability of 182 cycles, which was much higher than the 38 cycles sustained by the pristine LiCoO₂ cathode material when it was charged at 4.4 V.