Lithium Deintercalation Process Research Articles

Prospect and Status of Polyanionic Lithium Cobalt Silicates as High Energy‐Density and Safe Cathode Materials for Lithium‐Ion Batteries

Lithium cobalt silicate Li2CoSiO4 (LCSO) is a promising but challenging high energy‐density cathode for lithium‐ion battery. Herein, recent studies of synthesis–structure–performance of LCSO are reported, in which carbon coating, element doping, and nanostructure designs are incorporated in a two‐step synthesis starting with hydrothermal reaction. The initial performance is significantly improved with respect to previous reports in literature with the charge and discharge capacities now reaching 330 and 220 mAh g−1, respectively. The discharge voltage platform is compatible with the 4 V window of the nonaqueous organic electrolytes and presents no structural‐change‐induced voltage drops. The striking finding from the study of LCSO is the oxygen redox activity amid the second lithium deintercalation process, in which peroxo formation dominates the charge compensation to the high‐voltage lithium capacity. First‐principles modeling reveals an intrinsic and general relation between oxygen redox and cationic disorder in bulk compounds. Thus, LCSO is a new prototype of polyanionic materials with oxygen redox, which is the foundation of high‐capacity Li‐rich cathodes. This review is also aimed to narrate the progresses of LCSO within a broad domain of Li3PO4‐based polyanionic structures that support the development of solid‐state electrolytes for all solid‐state batteries.

Hydrothermal preparing agglomerate LiNi0.8Co0.1Mn0.1O2 cathode material with submicron primary particle for alleviating microcracks

Ni-rich layered oxides LiNixTM1-xO2 (TM = Co, Mn, Al, x > 0.6) cathode materials for lithium-ion batteries have an anisotropic volume change during lithium deintercalation process, which easily causes microcracks and rapid capacity decay. In the paper, carbonate precursor prepared by a urea-based hydrothermal method is lithiated at different temperatures of 750–850 °C to obtain agglomerate LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode material with different primary sizes. The sample synthesized at 750 °C shows broadening diffraction peaks due to its near-nano grain size, which results in the merging of (006)/(012) and (018)/(110) peaks. The effect of anisotropic volume shrinkage is effectively weakened by fine grain range, which alleviates formation of intergranular crack that is commonly considered as an important reason for capacity decay of Ni-rich layered oxide cathode materials. In addition, two new types of intragranular microcracks are first identified in cyclic NCM811. One extends along the spinel phase and layered phase interface, and the other extends along the vertical (003) R crystal plane. The difference in atomic plane spacing during the electrochemical cycles plays a key role in the growth of intragranular microcracks.

Antiferromagnetic ordering in lithium deintercalated Fe1−xZnxPO4: A Mössbauer spectroscopy study

Abstract Various compositions of Fe1−xZnxPO4 (x = 0.1, 0.2, 0.3, and 0.5) were synthesized by solid-state reaction and chemical lithium deintercalation processes, and their magnetic properties were characterized based on Mossbauer analysis. The synthesized Fe1−xZnxPO4 have orthorhombic structures with space group Pnma. The magnetization curves of Fe1−xZnxPO4 show the antiferromagnetic behaviors and magnetic phase transition caused by the strong crystal field in the FeO6 octahedral sites. The Neel temperature (TN) of Fe1−xZnxPO4 for x = 0.1, 0.2, 0.3, and 0.5 was found to be 97, 82, 63, and 62 K, respectively. Mossbauer spectra below TN appeared to have eight Lorentzian lines with antiferromagnetic ordering. The charge state of Fe ions is the high spin state of Fe3+, as characterized by an isomer shift (δ = 0.28–0.43 mm/s). The value of magnetic hyperfine field (Hhf) decreased with increasing Zn concentration because the superexchange interaction via Fe–O–Zn link is weaker than that via Fe–O–Fe link. Also, the value of electric quadrupole splitting (ΔEQ) gradually decreased with increasing Zn concentration due to the substitution of a Zn ion for the Fe ion, inducing a change in the charge asymmetry at the FeO6 sites. The Debye temperatures are found to decrease with increasing Zn concentration.

Insights in the electronic structure and redox reaction energy in LiFePO4 battery material from an accurate Tran-Blaha modified Becke Johnson potential

The main goals of this paper are to investigate the accuracy of the Tran-Blaha modified Becke Johnson (TB-mBJ) potential to predict the electronic structure of lithium iron phosphate and the related redox reaction energy with the lithium deintercalation process. The computed electronic structures show that the TB-mBJ method is able to partially localize Fe-3d electrons in LiFePO4 and FePO4 which usually is a problem for the generalized gradient approximation (GGA) due to the self interaction error. The energy band gap is also improved by the TB-mBJ calculations in comparison with the GGA results. It turned out, however, that the redox reaction energy evaluated by the TB-mBJ technique is not in good agreement with the measured one. It is speculated that this disagreement in the computed redox energy and the experimental value is due to the lack of a formal expression to evaluate the exchange and correlation energy. Therefore, the TB-mBJ is an efficient method to improve the prediction of the electronic structures coming form the standard GGA functional in LiFePO4 and FePO4. However, it does not appear to have the same efficiency for evaluating the redox reaction energies for the investigated system.

Direct Dry Synthesis of LiNi0.8Co0.2O2 Thin Film for Lithium Ion Battery Cathodes

In recent years, a number of cathode materials have been investigated for lithium ion battery applications. Transition metal oxides like LiCoO2 [1-2], LiNiO2 [3-4] and LiMn2O4 [5-6] have attracted much attention from researchers due to their stability and capacity to intercalate Li. LiCoO2 is commonly employed in commercial batteries as an intercalation compound because of its easiness in synthesis, high theoretical specific capacity and good reversibility. However, high toxicity and high cost are associated with the use of Co. Lithium nickel oxide and lithium manganese oxide are two feasible replacement materials for lithium cobalt oxide, but they come with challenges and limitations as well. LiMn2O4 reacts with the electrolyte when the temperature exceeds 55 °C, leading to dissolution of manganese and the loss of capacity [7]. In the case of LiNiO2 cathodes, its capacity is irreversibly lost when nickel oxide transforms from the hexagonal to the cubic phase during the lithium deintercalation process [8]. This phase transformation can be prevented by partially replacing nickel with cobalt, thus LiNixCo1− xO2 (0 < x < 1) could enhance the stability while adding the benefits of higher reversibility and lower cost [9-10]. It is also found from literature that when x is approximately 0.2, this material demonstrates better cycling properties than other materials mentioned above [11-13]. While solid state reactions and sol-gel methods have been widely used to synthesize LiNi0.8Co0.2O2 powders, there are many problems associated with these processes, such as structural inhomogeneity, multiple time consuming steps, irregular morphology and poor control of the particle size [14-16]. Reactive spray deposition technology (RSDT), a one-step flame based deposition method, offers a convenient solution to electrode fabrication by direct deposition of LiNi0.8Co0.2O2 nanoparticles. Films can be grown directly on the current collector. RSDT has the capability to tailor the electrochemical properties of synthesized cathode materials by manipulating the several key processing conditions. The size, morphology, and composition of particles can be controlled by changing the reactant concentration in the solvent, the heat enthalpy of solvent, the flow rate of precursor solution, and the flow rate of oxidant gases. Precursor solution for flame combustion is prepared by dissolving acetylacetonates of lithium, cobalt and nickel into organic solvents like methanol. X-ray diffraction (XRD), transmission electron microscopy (TEM) and inductively coupled plasma (ICP) are used to characterize the chemical composition, crystal structure, and structural morphology of the synthesized LiNi0.8Co0.2O2 nanoparticles. Electrochemical properties of as-deposited LiNi0.8Co0.2O2 thin film are evaluated with typical 2032 coin half-cell using lithium foil as the counter electrode. As the particle size of cathode material is in the nanometer range, the diffusion length of lithium ions is small, which enables a fast charge and discharge rate. The large surface area of the nanoparticles can also reduce the resistance of charge transfer.

Direct Dry Synthesis of LiNi0.8Co0.2O2 Thin Film for Lithium Ion Battery Cathodes

In recent years, a number of cathode materials have been investigated for lithium ion battery applications. Transition metal oxides like LiCoO2 [1-2], LiNiO2 [3-4] and LiMn2O4 [5-6] have attracted much attention from researchers due to their good recharge capabilities. LiCoO2 is commonly employed in commercial batteries as intercalation compound because of its easiness in synthesis, high theoretical specific capacity and good reversibility. However, high toxicity and high cost are associated with this material. Lithium nickel oxide and lithium manganese oxide are two feasible replacement materials for lithium cobalt oxide, but they come with challenges and limitations as well. LiMn2O4 reacts with electrolyte when the temperature exceeds 55 °C, leading to the loss of capacity from the dissolution of manganese [7]. In the case of LiNiO2 cathode, its capacity can be irreversibly lost when nickel oxide transforms from hexagonal to cubic phase during the lithium deintercalation process [8]. This phase transformation can be prevented by partially replacing nickel with cobalt, thus LiNixCo1− xO2 (0 < x < 1) is proposed with the aim of improving the stability of cathode material, while adding the benefits of high reversibility and low cost [9-10]. It is also found from literature that when x is approximately 0.2, this material performs the best electrochemically [11-13]. While solid state reactions and sol-gel methods have been widely used to synthesize LiNi0.8Co0.2O2 powders, there are many problems associated with these processes, such as inhomogeneity, multiple time consuming steps, irregular morphology and poor control of the particle size [14-16]. Reactive spray deposition technology, a one-step flame based deposition method in ambient environment, offers a convenient solution to electrode fabrication by direct deposition of LiNi0.8Co0.2O2 nanoparticles onto the current collector to form a thin film. This technique has the capability to tailor the electrochemical properties of synthesized cathode materials by manipulating the processing conditions. The size, morphology, and composition of particles can be controlled via deposition parameters, including the reactant concentration in the solvent, the heat enthalpy of solvent, the flow rate of precursor solution, and the flow rate of oxidant gases. Precursor solution for the flame combustion is prepared by dissolving acetylacetonates of lithium, cobalt and nickel into organic solvent like methanol. X-ray diffraction (XRD), transmission electron microscopy (TEM) and inductively coupled plasma (ICP) are used to characterize the chemical composition, crystal structure, and structural morphology of the synthesized LiNi0.8Co0.2O2 nanoparticles. Electrochemical properties of as-deposited LiNi0.8Co0.2O2 thin film are evaluated with typical 2032 coin half-cell using lithium foil as the counter electrode. As the particle size of cathode material is in the nanometer range, the diffusion length of lithium ions is small, which enables a fast charge and discharge rate. The large surface area of the nanoparticles can also reduce the resistance of charge transfer. In order to further investigate the electrochemical performance of the material, a coin full-cell using graphite as the anode is tested.

Mössbauer studies of olivine Fe1−y Mn y PO4

The olivine-structured Fe1−yMnyPO4 (y = 0.0, 0.1, and 0.3), a possible cathode material for lithium-ion secondary battery, has been studied by using x-ray diffraction (XRD) and Mossbauer spectroscopy. These Fe1−yMnyPO4 samples were prepared by using the chemical lithium deintercalation process from LiFe1−yMnyPO4. The crystal structures of the Fe1−yMnyPO4 samples were determined to be orthorhombic (space group Pnma) at room temperature by using the Rietveld refinement method. From the Mossbauer spectra at room temperature, the electric quadrupole splitting (ΔEQ) and the isomer shift (δ) values of the Fe1−yMnyPO4 were determined to be ΔEQ = 1.512 mm/s, and δ = 0.31 mm/s for y = 0.0, ΔEQ = 1.502 mm/s, and δ = 0.31 mm/s for y = 0.1, and ΔEQ = 1.382 mm/s, and δ = 0.31 mm/s for y = 0.3. The difference in the ΔEQ values for Fe1−yMnyPO4 samples with varying Mn concentrations can be explained by the change in the exchange interaction due to the dependence of the asymmetry in the FeO6 octahedral sites on the Mn concentration.

Kinetics of lithium deintercalation from LiFePO4

We have studied the kinetics of lithium deintercalation from lithium iron phosphate in a cathode material for batteries. The main contribution to the resistance of the cell is made by interfaces and the resistance of LiFePO4 grains. The FePO4 solubility in LiFePO4 is 4.0%. The lithium deintercalation process can be described in terms of a heterogeneous grain model and its rate is controlled by the lithium diffusion across the layer of the forming product (FePO4).

Electronic and electrochemical properties of Li xNi 1− yCo yO 2 cathode material

This studies are devoted to structural, electrical and electrochemical investigations of Li x Ni 1− y Co y O 2 system. A modification of electrical properties of the cathode material was observed upon deintercalation. A correlation between electronic properties and effectiveness of lithium deintercalation process was confirmed.

An electrochemical impedance spectroscopic study of the transport properties of LiNi 0.75Co 0.25O 2

Analysis of impedance spectra taken at closely spaced bias potential values on Li x Ni 0.75Co 0.25O 2 have been interpreted in terms of electronic and ionic transport properties of this electrode material. In the 0.9< x<1 range the material shows semi-conductive properties and the electronic conductivity dominates the transport. For x≤0.9, the properties change into those of a metal-like material in which the ionic conductivity becomes the limiting factor. The transition between these two limiting conditions clearly appears in the impedance spectra sequence. This transition is reversible since the same behaviour is observed during the lithium intercalation process as well as in the reverse lithium deintercalation process.

Structure and lithium deintercalation of Li 2− xRuO 3

Lithium deintercalation process of lithium ruthenium oxide, Li 2RuO 3, was characterized by X-ray diffraction and electrochemical measurements. The deintercalation proceeded from x = 0.0 to 1.3 with two-phasic reactions for 0 < x ≤ 0.5 and 0.7 ≤ x ≤ 1.0. Monophasic properties were observed for the compositions, Li 1.4RuO 3 and Li 0.9RuO 3; Li 1.4RuO 3 has a monoclinic cell isostructural to Li 2RuO 3, and Li 0.9RuO 3 has rhombohedral symmetry with the ilmenite-related structure. The lithium deintercalation from the lithium layer caused the rearrangement of the oxide-ion array from a cubic close packed (ccp) to a hexagonal close packed (hcp) structure. Further, electrical and magnetic properties were discussed on the basis of electrical and magnetic measurements.

Relationship between non-stoichiometry and physical properties in LiNiO 2

Lithium deintercalation process and magnetic properties were clarified for lithium nickel oxides with different sample compositions which were characterized by neutron and X-ray diffraction measurements. On deintercalation from the nearly stoichiometric “LiNiO 2” ( x−0.01 in Li 1− x− y Ni 1+ x O 2), a monoclinic phase appeared for 0.3 ≤ y ≤ 0.6. In contrast, no symmetry change from R 3 ̄ m was observed on deintercalation from the non-stoichiometric hosts of 0.05 ≤ x. The symmetry change from rhombohedral to monoclinic depends upon the degree of disorder in the host, LiNiO 2; the presence of “pillar” Ni ions in the Li layers prevents the lattice distortion. Magnetic behavior was significantly affected by the sample stoichiometry and their interactions were discussed on the basis of weak magnetic-field magnetization measurements.