Cathode Material In Lithium Cells Research Articles

Acoustic Emission Monitoring of High-Entropy Oxyfluoride Rock-Salt Cathodes during Battery Operation

High-entropy materials with tailorable properties are receiving increasing interest for energy applications. Among them, (disordered) rock-salt oxyfluorides hold promise as next-generation cathodes for use in secondary batteries. Here, we study the degradation behavior of a high-entropy oxyfluoride cathode material in lithium cells in situ via acoustic emission (AE) monitoring. The AE signals allow acoustic events to be correlated with different processes occurring during battery operation. The initial cycle proved to be the most acoustically active due to significant chemo-mechanical degradation and gas evolution, depending on the voltage window. Irrespective of the cutoff voltage on charge, the formation and propagation of cracks in the electrode was found to be the primary source of acoustic activity. Taken together, the findings help advance our understanding of the conditions that affect the cycling performance and provide a foundation for future investigations on the topic.

Atomic structural and electrochemical impact of Fe substitution on nano porous LiMnPO4

The atomic structural and electrochemical properties of Fe substituted nano porous LiMn1-xFexPO4 (x = 0–0.8) composites are investigated and compared. X-ray scattering method is used for atomic structural investigation. Rietveld refinement shows that all Fe substituted composites have the same olivine structure (Pnma) with lithium occupying octahedral 4a sites, Fe2+ replacing Mn2+ at the octahedral 4c sites. The a, b, c parameters and cell volume decrease with the addition of Fe2+. When the nano porous LiMn1-xFexPO4 composites are evaluated as cathode materials in lithium cells at room temperature, x = 0.6, and 0.8 resulted in the best overall electrochemical performance, exhibiting stable cycling and high discharge capacities of 149 and 154 mA h g−1, respectively. The composites with above x = 0.4 show a fast lithium ions transfer with high electronic conductivity because Fe transition metal substitution reduce the partly occupation of Mn in the M1 (LiO6) sites and thereby Mn block the lithium ion diffusion pathway. We here firstly find the antisite defect in the high Mn content in porous LiMn1-xFexPO4 composites.

A facile synthesis of Li2Fe1/3Mn1/3Ni1/3SiO4/C composites as cathode materials for lithium-ion batteries

The novel Li2Fe1/3Mn1/3Ni1/3SiO4/C has been successfully synthesized by a feasible solution process in ternary system. The spherical carbon-coated composites are obtained using a heat treatment in the presence of sucrose. X-ray diffraction (XRD) diffractogram displays that the Li2Fe1/3Mn1/3Ni1/3SiO4/C crystallized in an orthorhombic structure with a space group of Pmn21. The energy-dispersive X-ray spectroscopy mappings indicate that Fe, Mn and Ni elements are distributed homogenously in Li2Fe1/3Mn1/3Ni1/3SiO4/C nano-spherical particle with size less than 50 nm. The lithium storage capacity and cycling performance of the Li2Fe1/3Mn1/3Ni1/3SiO4/C presents good results when tested as cathode materials in lithium cells at room temperature. It delivers an initial discharge capacity of 181.4 mAh g−1 and a discharge capacity of 172.9 mAh g−1 after 20 cycles at 0.1C in the voltage range of 1.5–4.6V. Furthermore, it also exhibits an excellent rate capability with a capacity under different current densities of about 144.0 mAh g−1 (0.2 C), 117.9 mAh g−1 (0.5 C), 106.1 mAh g−1 (1 C), respectively and a good capacity cycling maintenance of 153.7 mAh g−1 after 60 cycles. Above results indicate that the spherical Li2Fe1/3Mn1/3Ni1/3SiO4/C becomes a very promising candidate for cathode material in lithium-ion batteries.

Synthesis and Electrochemical Performance of Li2MnSiO4/C as Cathode Materials with High Capacity for Lithium ion Batteries

Abstract Carbon-coated lithium manganese silicate (Li2MnSiO4/C) spherical composite particles were synthesized by solution process in a ternary system. X-ray diffraction (XRD) test of the obtained materials displays that the Li2MnSiO4 is crystallized in an orthorhombic structure with a space group of Pmn21. Scanning electron microscopy (SEM) images of the obtained samples show that the particles are spherical with less than 1 µm sizes. The composite prepared through ternary system shows good performance as cathode materials in lithium cells at room temperature. The charge capacity of the Li2MnSiO4/C samples is 310 mAh/g, and the discharge capacity is 286 mAh/g in the first cycle in the voltage range of 1.5–4.6 V. A good capacity cycling maintenance of 142 mAh/g after 30 cycles is obtained.

Effect of the iron doping in LiCoPO4 cathode materials for lithium cells

LiCoPO4 (LCP) is a promising candidate as alternative cathode for high-voltage lithium-ion batteries. However, its practical electrochemical performances are still far from the theoretical data likely due to the low electronic and ionic conductivities. Moreover LCP typically suffers a rapid capacity fading upon cycling, probably due to structural degradations and electrolyte decomposition at 5V vs. Li+/Li. Previous studies showed that carbon coating and metal doping may improve LCP electrochemical properties. In this work we report: (a) the fine tuning of a novel synthetic route at low temperature to obtain micrometric LCP crystallites morphologically homogeneous and crystallographically pure; (b) the analysis of the effect of iron doping on LCP structural features and electrochemical properties in lithium cell; (c) the beneficial simultaneous effect of iron doping and post-synthesis high-temperature annealing on the electrochemical performances in Li cells. The optimized material shows a reversible capacity of 120mAhg−1 at 0.1C rate and a capacity retention of 78% after 20 cycles.

Chromium substitution in ion exchanged Li 3Fe 2(PO 4) 3 and the effects on the electrochemical behavior as cathodes for lithium batteries

A new family of cathode materials for lithium cells with nominal stoichiometry Li 3Fe 2− x Cr x (PO 4) 3 (0 ≤ x ≤ 1), was successfully prepared by ion exchange reactions of Na 3Fe 2− x Cr x (PO 4) 3. The chemical exchange process leads to the structural transition from the monoclinic to a rhombohedral phase with an open framework which facilitates lithium diffusion. Chromium substitution was evidenced by a decrease in cell parameters in both sodium and lithium phases. 57Fe Mössbauer spectra revealed a decrease in the isomer shift on increasing Cr content. The partial substitution by low Cr contents improved the electrochemical performance of Li 3Fe 2− x Cr x (PO 4) 3. Thus, Li 3Fe 1.8Cr 0.2(PO 4) reversibly inserted 1.7 Li ions per formula unit, delivering a specific capacity of 105 mAh/g after the first discharge. The low electrode impedance of Cr substituted compounds can be responsible for the improvement of the electrochemical behavior.

Synthesis and electrochemical properties of Li2MnSiO4/C nanoparticles via polyol process

Carbon-coated lithium manganese silicate (Li2MnSiO4/C) nanoparticles were synthesized by polyol process. X-ray diffraction (XRD) patterns of the obtained materials exhibit a good fit with that of the Li2MnSiO4 phase. Field emission scanning electron microscopy (FESEM) images of the obtained samples show that the particle size is only tens of nanometers. The high resolution transmission electron microscopy (HRTEM) analysis shows that the Li2MnSiO4 nanoparticles are surrounded by a very thin film of amorphous carbon. The composite prepared through polyol process shows good performance as cathode materials in lithium cells at room temperature. The charge capacity of the Li2MnSiO4/C samples is 219 mAh/g (about 1.3 Li+ per unit formula extracted), and the discharge capacity is 132 mAh/g (about 0.8 Li+ per unit formula inserted) in the first cycle in the voltage range of 1.5–4.8 V. A good capacity cycling maintenance of 81.8% after 10 cycles was obtained.

Polyterthiophene/CNT composite as a cathode material for lithium batteries employing an ionic liquid electrolyte

A polyterthiophene (PTTh)/multi-walled carbon nanotube (CNT) composite was synthesised by in situ chemical polymerisation and used as an active cathode material in lithium cells assembled with an ionic liquid (IL) or conventional liquid electrolyte, LiBF 4/EC–DMC–DEC. The IL electrolyte consisted of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF 4) containing LiBF 4 and a small amount of vinylene carbonate (VC). The lithium cells were characterised by cyclic voltammetry (CV) and galvanostatic charge/discharge cycling. The specific capacity of the cells with IL and conventional liquid electrolytes after the 1st cycle was 50 and 47 mAh g −1 (based on PTTh weight), respectively at the C/5 rate. The capacity retention after the 100th cycle was 78% and 53%, respectively. The lithium cell assembled with a PTTh/CNT composite cathode and a non-flammable IL electrolyte exhibited a mean discharge voltage of 3.8 V vs Li +/Li and is a promising candidate for high-voltage power sources with enhanced safety.

Preparation and Electrochemistry of Silver Vanadium Phosphorous Oxide, Ag[sub 2]VO[sub 2]PO[sub 4

Recently, there has been interest in phosphate cathodes for lithium batteries due to the excellent chemical and thermal stability of LiFePO 4 . Vanadium oxide bronzes have attracted attention due to silver vanadium oxide (Ag 2 V 4 O 11 ) batteries being used as power implantable devices. We report the first investigation of silver vanadium phosphorous oxide (Ag 2 VO 2 PO 4 ) as a cathode material in lithium cells. While the synthesis of Ag 2 VO 2 PO 4 has been previously reported, this is the first exploration of its electrochemistry. The Ag 2 VO 2 PO 4 material yielded 205 mAh/g to 2.0 V and 270 mAh/g to 1.5 V under constant current discharge and supported 50 mA/cm 2 pulses above 1.5 V.

Enhancement of electrochemical performance of lithium iron phosphate by controlled sol–gel synthesis

The porous phase pure lithium iron phosphate (LiFePO 4/C) composite particles with a few nanometers thick layer of carbon were synthesized by sol–gel method. The in situ coating of carbon on the LiFePO 4 particles was achieved by the pyrolysis of carbon source during the thermal treatment. The synthetic conditions were observed to affect physical, morphological and electrochemical properties of the composites. The composite synthesized via a single-step thermal treatment at 700 °C in the presence of a mixture of citric acid and sucrose possesses a large surface area and porous structure. The structure of the residual carbon coated in this sample is observed to be graphene-rich with the lowest D/G (disordered/graphene) ratio in the Raman spectra. When the three LiFePO 4/C composites were evaluated as cathode materials in lithium cells at room temperature, the composite prepared in the presence of sucrose as an additional carbon source showed the highest electrochemical performance exhibiting high discharge capacities of 153 (corresponding to 90% of the theoretical capacity), 120, 112, and 94 mAh/g at 0.1, 1, 3, and 5 C-rates, respectively.

Electrochemical properties of carbon-coated LiFePO 4 synthesized by a modified mechanical activation process

Carbon-coated lithium iron phosphate (LiFePO 4/C) composites were synthesized by conventional mechanical activation (MA) process and also by a modified MA process. Phase-pure particles were obtained of ∼100 nm size with a nano-meter thick web of carbon surrounding the particles. The composite prepared by the modified MA process shows good performance as cathode material in lithium cells at room temperature. A high performance was achieved at 0.1 C-rate with >96% utilization of the active material. A stable cycle performance even at higher C-rates was achieved with a cathode that has a total carbon content of only 12 wt%. The use of the modified MA process to synthesize LiFePO 4/C has promise to be an efficient process to decrease the total carbon content of the cathode, resulting in the enhanced energy density.

Lithium storage in conductive sulfur-containing polymers

Conductive sulfur-containing cathode materials for high-capacity lithium secondary batteries have been synthesized by heating a mixture of polyacrylonitrile and elemental sulfur. The structures and electrochemical properties of the materials depend on the reaction conditions, particularly synthesis temperatures. FTIR, Raman and XPS measurements show that the fundamental chemical structure of the materials is composed of a dehydropyridine type matrix with S–S bonds in the side-chain. The cycle performances of the materials synthesized at different temperatures have been examined as active cathode materials in lithium cells. Due to the existence of π-conjugation and the C–S–S–C covalent bond, significantly improved redox rates and cycleability at room temperature are achieved. A stable discharge capacity for the material synthesized at 450 °C is maintained at about 480 mAh/g and the capacity retention remains at ca. 92% (referred to the second cycle) after about 240 cycles. The excellent cycle characteristics supply a good foundation for practical application of this material in rechargeable lithium batteries.

Understanding the voltage profile of Li insertion into LiNi 0.5− yFe yMn 1.5O 4 in Li cells

LiNi 0.5− y M y Mn 1.5O 4 compounds have proven to be of great interest as active cathode material for high-voltage lithium-ion cells. The electrochemical behavior of LiNi 0.5− y Fe y Mn 1.5O 4 compounds as cathode material in lithium cells is studied here. The charge–discharge curves are characterized by three main plateaus, ascribable to the removal (during charge) or filling (during discharge) of d electrons corresponding to the different redox pairs present: Fe IV/Fe III, Ni IV/Ni II and Mn IV/Mn III. Taking into account the entropy associated to the lithium extraction/insertion and the filling of the different electronic levels, the modelization gives a good reproducibility of the experimental electrochemical curves. The standard potential μ 0 of the redox pairs were estimated to be ca. −4.90, −4.80 and −4.23 eV, respectively.

A study of layered lithium manganese oxide cathode materials

Substituted layered sodium manganese oxide bronzes with the P2 structure were prepared by glycine-nitrate combustion synthesis. The Na in the as-prepared materials could be completely ion-exchanged for Li under mild conditions. All lithium manganese oxide compounds obtained after ion-exchange have O2 stacking of the layers. Cyclic voltammetry and stepped potential experiments on lithium cells containing these materials show that the main redox reaction around 3.1 V is a diffusion-controlled process and is completely reversible. O2-Li 0.6[Al 0.1Mn 0.85□ 0.05]O 2 and O2-Li 0.6[Ni 0.1Mn 0.85□ 0.05]O 2 are particularly promising as cathode materials in lithium cells because of the high reversible discharge capacities (180 mAh/g).

Sulfur-rich copolymers of sulfur with 5-vinylbicyclo[2.2.1]hept-2-ene and tricyclo[5.2.1.0 2.6]deca-3,8-diene as prospective cathode materials for lithium cells

Catalytic copolymerization of sulfur with 5-vinylbicyclo[2.2.1]hept-2-ene or tricyclo[5.2.1.0 2.6 ]deca-3,8-diene (sulfur:diene ratio=20:1) at 170 v °C in bulk or decalin in the presence of 1,4-diazabicyclo[2.2.2]octane or N,N,N,N-tetramethylethylenediamine in combination with CoCl 2 - 6H 2 O or Cu(acac) 2 occurs at two dienic double bonds to form partially cross-linked copolymers stable up to 200 v °C (DSC/TGA). Preliminary evaluation of the specific discharge capacity of cathodes made using the above copolymers in model lithium button cells gives 670-970 and 300-330 v mA - h - g m 1 in the 1st and 50th cycles, respectively.

Control of the structure and properties of vanadium and manganese oxides through tailored soft synthesis

Vanadium and manganese oxides can be readily synthesized using soft chemical approaches, such as hydrothermal, sol–gel, intercalation and ion-exchange. By controlling the pH and organic reactants/templates it is possible to control the structure formed by controlling the species in solution. In the case of vanadium, its coordination number increases as the pH decreases. It is found that the higher the vanadium coordination number the better the behavior of the oxide as a cathode material in lithium cells; tetrahedral vanadium is not reduced without destruction of the structure, whereas octahedral vanadium as in the delta double sheet structure holds its structure during reduction. Manganese oxides can also be synthesized using hydrothermal methods, with layered structures formed when small cations are present and tunnel structures when larger cations or anions are present. A range of mixed vanadium manganese oxides has been prepared, the structure depending on the organic cation and vanadium-to-manganese ratio. In several cases these are pillared oxides, that readily react with intercalating cations.

Structural Characterization and Electrochemical Reactions with Lithium of Cu2CoTixSn3-xS8 Solid Solutions

The synthesis, structural determination, and electrochemical studies of Cu2CoTixSn3-xS8 solid solutions are reported. The evolution of the cubic spinel unit cell parameter with x shows two regions which are defined by the increasing covalency of the Ti−S bonds and the radii of the metal ions present in the solid. An increase in the isomer shift of the 119Sn Mössbauer spectra of these solids agrees with this interpretation. The solid solutions are used as active cathode materials in lithium cells. The discharge shows a complex reduction effect which is associated with the decrease in the oxidation state of Sn4+ and Ti4+ ions, accompanied by deep structural changes which end in the complete amorphization of the solid and the occurrence of tin in the metallic state. The extended discharge of the lithium cells leads to a good cycling behavior in galvanostatic experiments carried out in the 0−2.3 V interval, with capacities close to 400 mAh/g after 10 cycles.

Lithium−Nickel Citrate Precursors for the Preparation of LiNiO2 Insertion Electrodes

Noncrystalline solids with LiNi(C6H4O7)3/4·xH2O, LiNi(C6H5O7)·xH2O, and (NH4)3LiNi(C6H5O7)2·xH2O (x ≈ 5) chemical compositions were obtained by freeze drying of concentrated lithium−nickel−citrate solutions. The IR spectra of solid citrates reveal that triionized citrate ions chelate the Ni2+ ions with their carboxylate groups acting as monodentate agents. Electronic spectra reveal monomeric 1:1 Ni(II)−citrate(−3) complexes in the mixed citrate powders. Finely disperse layered Li1-xNi1+xO2 solids were obtained by the thermal decomposition of the citrate precursors at 700−800 °C in an oxygen atmosphere. Almost stoichiometric Li1-xNi1+xO2 (x ≤ 0.05) oxides with layered R3m structure are obtained from monocitrate precursors. The LiNiO2 powder were used as active cathode material in lithium cells. Cyclic voltammograms showed several current peaks during the first cycle resulting from the formation of the intermediate phases usually found in quasi-stoichiometric LiNiO2. After the almost complete extraction of...

Fluorine reactivity with graphite and fullerenes. fluoride derivatives and some practical electrochemical applications

Abstract The reactivity of fluorine with graphite depends strongly on reaction temperature and purity of the fluorine atmosphere. The presence of fluoride impurities accelerates the reaction even at room temperature. The CF bond character ranges from covalent to ionic or semi-ionic. The electrochemical performance of fluorinated graphite products as cathode material in lithium cells is related to lamellar structure, ionicity and fluorine content. Unlike graphite, fullerenes react readily with pure fluorine even at room temperature. Highly fluorinated C 60 compounds of high crystallinity are obtained at 300 °C. A fully fluorinated product C 60 F 60 can also be isolated.

Synthesis, Characterization, and Electrochemical Performances of Substituted Layered Transition Metal Oxides. LiM1-yM'yO2. (M=Ni and Co. M'= B and AI)

AbstractThe synthesis, characterization and electrochemical performances of lithiated nickelate and cobaltate doped with Al and B are reported. The synthesis involves solid state reaction between lithium hydroxide, nickel or cobalt oxides and several sources of aluminum and boron. Careful selection of precursors and heat treatment conditions are required to prepare single phase impurity free samples. X-ray diffraction and Rietveld refinement analysis indicate that the layered structure is preserved upon considerable substitution of aluminum and boron. X-ray diffraction line intensities and positions remained in good agreement with the space group. The IR spectra of the samples indicate formation of compressed CoO6 and NiO6, and elongated LiO6 octahedra. The IR vibrational mode of the LiO6 remains in the 200–300 cm-1 and the vibrational modes of the MO6 expand over 400–650 cm-1. Results of long charge-discharge cycling of the samples as cathode materials in lithium cells showed long cycle life. The capacity of the electrodes upon substitution were reduced almost linearly as the concentration of substitution was increased. The solubility limit for the formation of solid solutions upon substitution of Al and B in LiNiO2 and LiCoO2 was found to be around 25%. Specific capacities of the samples were between 120 to 160 mAh/g depending on the amount of substitution.