FePO4 Research Articles

Elucidating the Impact of Mn-Fe Substitution on The Crystal Structure of LiMn(x)Fe(1-x)PO4 Solid Solutions: A Theoretical Study

Abstract This study generated crystallography information files (CIF) to synthesize LiMn(x)Fe(1-x)PO4 solid solutions, with the Mn to Fe substitution ratio (x) ranging from 0 to 1 in 0.1 increments, guided by Vegard’s law, utilizing crystallography software. The investigation focused on how this substitution influences key structural parameters and properties within the Mn-Fe Olivine system. Specifically, it examined variations in lattice parameters, unit cell volume, cell density, and Theoretical capacity attributable to the substitution factor. Furthermore, X-ray diffraction (XRD) patterns, predicted using mathematical models through the same software, provided insights into structural changes. Notably, the XRD analysis revealed a progressive shift in peak positions and an increase in peak intensities corresponding to the substitution level. These observations were linked to the altered lattice parameters resulting from the introduction of ions with varying ionic radii, and an enhanced electron density stemming from the increased presence of Fe. This comprehensive analysis underscores the significant impact of Mn-Fe replacement on the microstructural characteristics and electron density of the olivine system, offering valuable insights into material design and optimization in the context of energy storage materials.

FePO4 activated sulfite autoxidation for simultaneous pollutant degradation and phosphorus release

FePO4 (FP) as a precursor of lithium iron phosphate batteries has been mass-produced in recent years and may face the problem of overproduction. Also, the phosphorus removal process in wastewater treatment plants produces large amounts of sludge containing FP. It is a huge waste of both iron and phosphorus resources if such FP cannot be utilized. This work explores a new strategy for utilizing FP to activate sulfite (S(IV)) autoxidation for simultaneous pollutant degradation and phosphorus release in water. Acid orange 7 (AO7) and several pharmaceutical and personal care products (PPCPs) were chosen as the target pollutants for the FP‒S(IV) system and the influence of pH, FP and S(IV) dosage were investigated. Typically, up to 89.5% AO7 (10 mg L−1) and above 60% PPCPs (10 μM) were oxidized within 90 min by adding 1 g L−1 FP and 2 mM S(IV) into the water at the initial pH 4.0. Results of quenching experiments and electron spin resonance analysis confirmed SO5•− as the dominant reactive species for AO7 oxidation. Meanwhile, two stages of phosphorus release from FP were observed along with the AO7 oxidation and their linear correlation over the pH range 3.0–8.0 was proven. The first stage (0–5 min) was thought to be dependent on the initial pH and was obviously faster than the second stage (10–45 min), whose rate increased linearly with S(IV) dosage. Phosphorus released high up to 24.3 μM at 90 min with 4 mM S(IV). Moreover, the mechanisms of FP activated sulfite autoxidation as well as phosphorus release were proposed, and the AO7 degradation pathway was investigated. This study provides a novel possibility for FP waste utilization and potential recovery of phosphorus resources.

Dynamic Li+ Capture through Ligand-Chain Interaction for the Regeneration of Depleted LiFePO4 Cathode.

After application in electric vehicles, spent LiFePO4 (LFP) batteries are typically decommissioned. Traditional recycling methods face economic and environmental constraints. Therefore, direct regeneration has emerged as a promising alternative. However, irreversible phase changes can significantly hinder the efficiency of the regeneration process owing to structural degradation. Moreover, improper storage and treatment practices can lead to metamorphism, further complicating the regeneration process. In this study, a sustainable recovery method is proposed for the electrochemical repair of LFP batteries. A ligand-chain Zn-complex (ZnDEA) is utilized as a structural regulator, with its ─NH─ group alternatingly facilitating the binding of preferential transition metal ions (Fe3+ during charging and Zn2+ during discharging). This dynamic coordination ability helps to modulate volume changes within the recovered LFP framework. Consequently, the recovered LFP framework can store more Li-ions, enhance phase transition reversibility between LFP and FePO4 (FP), modify the initial Coulombic efficiency, and reduce polarization voltage differences. The recovered LFP cells exhibit excellent capacity retention of 96.30% after 1500 cycles at 2C. The ligand chain repair mechanism promotes structural evolution to facilitate ion migration, providing valuable insights into the targeted ion compensation for environmentally friendly recycling in practical applications.

Simultaneous anodic de-lithiation/cathodic lithium-embedded regeneration method for recycling of spent LiFePO4 battery

The widespread use of lithium-ion batteries for energy storage will result in millions of tons of scrapped LiFePO4 (LFP) batteries. Current recycling technologies for LFP cathode materials require harsh acid treatments and are expensive. Hence, in this work, an ingenious electrochemical method is developed to recycle scrapped LFP. Specifically, through the charging/discharging process of an electrolytic system in which both the cathode and anode are scrapped LFP, the anode is de-lithiated to obtain FePO4 (FP), meanwhile, the Li+ from the anode is embedded into the cathode scrapped LFP to achieve regeneration. The experimental results show that the anode de-lithiation rate is 92 % and the cathode regeneration performance is closely related to the driving voltage. A voltage of 1 V converts the FP phase to LFP and effectively eliminates the LFP defect lattice. However, an excessive voltage (1.2 V) leads to an extremely fragile LFP crystal structure, resulting in the ineffective embedment of Li+ into the defective lattice and ineffective capacity restoration. The regenerated LFP exhibits a high restored capacity (136.5 mAh g−1 at 1 C) and excellent stability (95.32 % capacity retention after 300 cycles at 5 C). This novel method does not require an additional Li source, consumes low electrical energy (31.9 kWh t−1) and has a high current efficiency (>98 %), and it yields economic and environmental benefits that will contribute to the sustainable development of the LFP industry.

Turbulence induced shear controllable synthesis of nano FePO4 irregularly-shaped particles in a counter impinging jet flow T-junction reactor assisted by ultrasound irradiation

FePO4 (FP) particles with a mesoporous structure amalgamated by nanoscale primary crystals were controllably prepared using an ultrasound-intensified turbulence T-junction microreactor (UTISR). The use of this type of reaction system can effectively enhance the micro-mixing and remarkably improve the mass transfer and chemical reaction rates. Consequently, the synergistic effects of the impinging streams and ultrasonic irradiation on the formation of mesoporous structure of FP nanoparticles have been systematically investigated through experimental validation and CFD simulation. The results revealed that the FP particles with a mesoporous structure can be well synthesised by precisely controlling the operation parameters by applying ultrasound irradiation with the input power in the range of 0–900 W and the impinging stream volumetric flow rate in the range of 17.15–257.22 mL·min−1. The findings obtained from the experimental observation and CFD modelling has clearly indicated that there exists a strong correlation between the particle size, morphology, and the local turbulence shear. The application of ultrasonic irradiation can effectively intensify the local turbulence shear in the reactor even at low Reynolds number based on the impinging stream diameter (Re < 2000), leading to an effective reduction in the particle size (from 273.48 to 56.1 nm) and an increase in the specific surface area (from 21.97 to 114.97 m2·g−1) of FP samples. The FPirregularly-shaped particles prepared by UTISR exhibited a mesoporous structure with a particle size of 56.10 nm, a specific surface area of 114.97 m2·g−1and a total pore adsorption volume of 0.570 cm3·g−1 when the volumetric flow rate and ultrasound power are 85.74 mL·min−1and 600 W, respectively.

Characteristic of phosphorus rich compounds in the incinerated sewage sludge ashes: a case for sustainable waste management

Growing concern over mineral resources supply forces us to search for alternative sources of Phosphorus. The possibility to recover phosphorus from incinerated sewage sludge ashes appears to be an important aspect in anthropogenic phosphorus cycle and sustainable economy. To make phosphorus recovery efficient it is important to learn the chemical and mineral composition of ash and phosphorus speciation. The phosphorus content in the ash was over 7%, what corresponds to medium rich phosphorus ores. The main phosphorus rich mineral phases were phosphate minerals. The most widespread was tri-calcium phosphate Whitlockite with various Fe, Mg and Ca proportions. In minority Fe–PO4 and Mg–PO4 were detected. Whitlockite commonly overgrown with hematite, influences negatively mineral solubility and thus recovery potential and indicates low bioavailability of phosphorus. Considerable amount of phosphorus was found in the low crystalline matrix where phosphorus content was around 10 wt% however low crystallinity and dispersed phosphorus also does not strengthen the potential to recover this element.

Direct regeneration and performance of spent LiFePO4 via a green efficient hydrothermal technique

With the quick development of electric vehicles and grid energy storage, the demand and production of lithium ion batteries (LIBs) are rapidly increasing, and the problem of lithium resource shortage becomes more and more serious. Both in terms of economic value and environmental protection, the recycling and regeneration of the spent lithium batteries is extremely urgent. Herein, a green and efficient hydrothermal technique for direct regeneration of spent lithium iron phosphate (LiFePO4 or LFP) was proposed. LFP loses the partial lithium during the long cycle and converts to FePO4 (FP), therefore, the replacement of the lost lithium is crucial for the regeneration of spent LFP. Herein, the effects of hydrothermal conditions such as reaction temperature, Li+ concentration and reducing agent concentration on the performance of product are systemically studied. Besides, it has been found that the control of hydrothermal condition is conductive to the supplement of Li and the enhancement of electrochemical performance of the product. Under hydrothermal conditions of 200 °C for 3 h, the regenerated LFP shows the optimal electrochemical performance of 165.9, 151.93, 145.92, 133.11 and 114.96 mAh g−1 at 0.1, 0.5, 1, 2, and 5 C, respectively. In addition, the capacity retention is as high as 99.1% after 200 cycles at 1 C. Therefore, this work provides a new idea for the direct regeneration of spent LFP cathode materials.

Nano-LiFePO4/C Derived from Gaseous-Oxidation Engineering-Synthesized Amorphous Mesoporous nano-FePO4 for High-Rate Li-Ion Batteries

Fast charging/discharging capabilities are highly desirable for Li-ion batteries (LIBs). LiFePO4 as a low-cost material is widely used in LIBs. However, the poor electronic and ionic conductivity hinder its rate performance. Herein, a continuous ozone-oxidation strategy is successfully used to prepare amorphous mesoporous nano-FePO4 (O3-FP), which is then used to synthesize high-performance nano-LiFePO4/C (nano-LFP/C). The continuous ozone bubbles are the key to oxidize the Fe(II) salts and restrain the aggregation of precipitated nanoparticles benefiting from the gas bubble confinement effect and a higher ζ potential. The obtained O3-FP shows a smaller and more uniform particle size, and a larger surface area than the conventional liquid oxidation-prepared FePO4 (FP). The O3-FP-derived nano-LFP/C exhibits a uniform carbon coating, a smaller and more even particle size, and better electrochemical performance. When used as cathode for LIBs, the optimized electrode delivers a high capacity of 160 mAh g–1 at 1C and 78 mAh g–1 at an ultrahigh rate of 150C. Moreover, it also possesses excellent high- and low-temperature performance. The uniform-carbon-coating nano-LFP/C developed in this research is simple, scalable, and environmentally benign, making it promising for mass production of nano-LFP/C.

Coupled Li-P Zoning and Trace Elements of Olivine from Magmatic Ni-Cu Deposits: Implications for Postcumulus Re-Equilibration in Olivine

Abstract Olivine is an important mineral in mafic–ultramafic rocks and records various crustal and mantle processes in basaltic magma. Generally, phosphorus (P) is immobile in olivine and its zoning tends to record magmatic processes. In contrast, lithium (Li) is one of the most mobile elements in olivine and tends to be re-distributed by postcumulus to hydrothermal processes. This study reports coupled Li-P oscillatory and sector zoning in cumulus olivine (Fo &amp;gt; 80 mol%) from magmatic Ni-Cu deposits in northwest China. The close to 1:1 relationship between Li + Na cation and P cation in olivine suggests P substitutes for slowly diffusing Si at the tetrahedral site and Li (Na) substitutes for Mg at the octahedral metal site. The preservation of such coupled Li-P zoning suggests that the charge-balanced–controlled substitution of Li+P5+ for Mg2+Si4+, producing a member of the Li(Fe)PO4 structure, may cause sluggish Li diffusion in olivine. The Li-P zoning is uncorrelated to other elements (Fe, Mg, Cr, Al, Ca, Ti, V, Ni, Zn, Mn, Co, and Sc). The Ca abundances in cumulus olivine are significantly depleted relative to those in volcanic olivine and modeled for olivine using the rhyolite–MELTS program, whereas the Mg, Fe, Mn, Zn, Ni, and Co contents show no signs of depletion. The Cr and Al contents in high Fo olivine are lower than those in volcanic olivine with a similar Fo value. The depletions in Ca, Cr, and Al (both divalent and trivalent cations) have been attributed to post-crystallization re-equilibration processes. We suggest that the selective Ca-Cr depletion in olivine resulted from re-equilibration between olivine and clinopyroxene–orthopyroxene–spinel–melts at the postcumulus stage, whereas the Al content variation in olivine is likely controlled by olivine–spinel (pyroxene) re-equilibration. Olivine fractionation modeling results reveal that Co content in both olivine and sulfides changes slightly during evolution, whereas the olivine Ni/Co ratio decreases dramatically from 30 (at Fo90) to 4 (Fo80). These are consistent with the variation of Ni and Co contents in olivine from sulfide-barren rocks but cannot explain the strong positive Ni-Co correlation observed in olivine from the sulfide-bearing rocks. The considerable increase in the Ni/Co ratio in olivine coexisting with the high Ni tenor sulfide compared with the slight increase of the Ni/Co ratio in olivine coexisting with moderate-low Ni tenor sulfide strongly suggests that the Ni and Co contents and Ni/Co ratio in olivine from the mineralized rocks were the results of olivine–sulfide interaction. The olivine Fe/Zn and Mn/Zn ratios show little difference between sulfide-barren and sulfide-rich rocks, but these ratios decrease considerably with the decreasing Fo values. Overall, the study suggests that elements (Ca, Cr, Al, Mg, Fe, Ni, Co, Zn, etc.) diffuse faster than P have been re-distributed in cumulus olivine by re-equilibration processes, modifying the elemental content and inter-element ratios in olivine. The characteristics of the crystallization, particularly the source recorded in cumulus olivine, may be obscured and overprinted by postcumulus processes.

Cobalt-Iron-Phosphate Hydrogen Evolution Reaction Electrocatalyst for Solar-Driven Alkaline Seawater Electrolyzer.

Seawater splitting represents an inexpensive and attractive route for producing hydrogen, which does not require a desalination process. Highly active and durable electrocatalysts are required to sustain seawater splitting. Herein we report the phosphidation-based synthesis of a cobalt–iron–phosphate ((Co,Fe)PO4) electrocatalyst for hydrogen evolution reaction (HER) toward alkaline seawater splitting. (Co,Fe)PO4 demonstrates high HER activity and durability in alkaline natural seawater (1 M KOH + seawater), delivering a current density of 10 mA/cm2 at an overpotential of 137 mV. Furthermore, the measured potential of the electrocatalyst ((Co,Fe)PO4) at a constant current density of −100 mA/cm2 remains very stable without noticeable degradation for 72 h during the continuous operation in alkaline natural seawater, demonstrating its suitability for seawater applications. Furthermore, an alkaline seawater electrolyzer employing the non-precious-metal catalysts demonstrates better performance (1.625 V at 10 mA/cm2) than one employing precious metal ones (1.653 V at 10 mA/cm2). The non-precious-metal-based alkaline seawater electrolyzer exhibits a high solar-to-hydrogen (STH) efficiency (12.8%) in a commercial silicon solar cell.

Zero Lithium Miscibility Gap Enables High-Rate Equimolar Li(Mn,Fe)PO4 Solid Solution.

Forming olivine-structured Li(Mn,Fe)PO4 solid solution is theoretically a feasible way to improve the energy density of the solid solutions for lithium ion batteries. However, the Jahn-Teller active Mn3+ in the solid solution restricts their energy density and rate performance. Here, as demonstrated by operando X-ray diffraction, we show that equimolar LiMn0.5Fe0.5PO4 solid solution nanocrystals undergo a single-phase transition during the whole (de)lithiation process, with a feature of zero lithium miscibility gap, which endows the nanocrystals with excellent electrochemical properties. Specifically, the energy density of LiMn0.5Fe0.5PO4 reaches 625 Wh kg-1, which is 16% higher than that of LiFePO4. Moreover, the high-performance LiMn0.5Fe0.5PO4 nanocrystals are prepared by a microwave-assisted hydrothermal synthesis in pure water.

Flotation Separation of Chalcopyrite and Molybdenite Assisted by Microencapsulation Using Ferrous and Phosphate Ions: Part I. Selective Coating Formation

Porphyry Cu-Mo deposits, which are the most important sources of copper and molybdenum, are typically processed by flotation. In order to separate Cu and Mo minerals (mostly chalcopyrite and molybdenite), the strategy of depressing chalcopyrite while floating molybdenite has been widely adopted by using chalcopyrite depressants, such as NaHS, Na2S, and Nokes reagent. However, these depressants are potentially toxic due to their possibility to emit H2S gas. Thus, this study aims at developing a new concept for selectively depressing chalcopyrite via microencapsulation while using Fe2+ and PO43− forming Fe(III)PO4 coating. The cyclic voltammetry results indicated that Fe2+ can be oxidized to Fe3+ on the chalcopyrite surface, but not on the molybdenite surface, which arises from their different electrical properties. As a result of microencapsulation treatment using 1 mmol/L Fe2+ and 1 mmol/L PO43−, chalcopyrite was much more coated with FePO4 than molybdenite, which indicated that selective depression of chalcopyrite by the microencapsulation technique is highly achievable.

Controllable synthesis of hierarchical micro/nano structured FePO4 particles under synergistic effects of ultrasound irradiation and impinging stream

Hierarchical micro/nano-structured FePO4 (FP) particles were environmental-friendly and controllable synthesized through synergistic intensification of ultrasound and impinging streams. Nano-scale FP seeds were firstly synthesized via ultrasound irradiation intensified impinging stream reaction (UISR), where the enhanced turbulent micromixing in the impinging streams benefits the nucleation process while the application of ultrasound to the impinging streams further intensifies such micromixing. The ultrasound frequency and power applied were 20 kHz and 600 W. The hierarchical micro/nano-structured FP particles are obtained when taking sufficient reaction time and stirring FP nano-seeds in a continuous stirring tank reactor (CSTR). Effects of the sonochemical pre-treatment, mean residence time and rotation speed on the physical-chemical properties of FP were investigated systematically. The characterization revealed that under the optimum operating condition, the FP particles presented near-spherical hierarchical micro/nano-structure, consisting of nanoscale primary grains. The mechano-chemical effects on the synthesized FP particles during different synthesis process were also studied.

Phase Transformation of Doped LiCoPO4 during Galvanostatic Cycling.

In situ X-ray diffraction was employed to investigate the crystal structure changes in Cr/Si co-doped Li(Co,Fe)PO4 cathode material during a galvanostatic charge/discharge process at a slow rate of C/30. The evolution of the X-ray patterns revealed that the phase transformation between the Cr/Si-Li(Co,Fe)PO4 and Cr/Si-(Co,Fe)PO4 is a two-step process, which involves the formation of an intermediate compound of Cr/Si-Li0.62(Co,Fe)PO4 upon the extraction of Li ions from the pristine phase. Different from the previously reported two biphasic transition steps, the phase transformation of the Cr/Si-Li(Co,Fe)PO4 followed a solid solution and a biphasic reaction pathway at different stages of the delithiation/lithiation process, respectively.

Phase-field modeling of Li-insertion kinetics in single LiFePO4-nano-particles for rechargeable Li-ion battery application

We develop a continuum phase-field model for the simulation of diffusion limited solid-solid phase transformations during lithium insertion in LiFePO4-nano-particles. The solid-solid phase boundary between the LiFePO4 (LFP)-phase and the FePO4 (FP)-phase is modeled as a diffuse interface of finite width. The model-description explicitly resolves a single LiFePO4-particle, which is embedded in an elastically soft electrolyte-phase. Furthermore, we explicitly include anisotropic (orthorhombic) and inhomogeneous elastic effects, resulting from the coherency strain, as well as anisotropic (1D) Li-diffusion inside the nano-particle. In contrast to other related research work, we employ an Allen-Cahn-type phase-field approach for the diffuse interface modeling of the solid-solid phase boundary. The model contains an extra non-conserved order parameter field to distinguish the two different phases. The evolution of this order parameter field is controlled by an extra kinetic parameter independent from the Li-diffusion. Further, the effect of the nano-particle’s size on the kinetics of FP to LFP phase transformations is investigated by means of both model. Both models predict a substantial increase in the steady state transformation velocity as the particle-size decreases down to dimensions that are comparable with the width of the interface between the FP and the LFP-phase. However, the extra kinetic parameter of the Allen-Cahn-type description may be used to reduce the strength of the velocity-increase with the decreasing particle size. Further, we consider the influence of anisotropic and inhomogeneous elasticity on the lithiation-kinetics within a rectangularly shaped LiFePO4-particle embedded in an elastically soft electrolyte. Finally, the simulation of equilibrium shapes of LiFePO4-particles is discussed. Within a respective feasibility study, we demonstrate that also the simulation of strongly anisotropic particles with aspect ratios up to 1/5 is possible.

Evolution and Migration of Lithium-Deficient Phases during Electrochemical Delithiation of Large Single Crystals of LiFePO4

In a lithium ion battery, lithiation and delithiation of active materials occur during charging and discharging, and diffusion of Li (or Li vacancy) and related phase transformation in the active material greatly affect battery performance. Evolution and migration of Li-deficient phases at surfaces of single crystals of LiFePO4 (2 × 3 × 6 mm in size) during electrochemical delithiation were studied by using Raman microscopy and in situ wide-view scanning Raman spectroscopy. Domains of phases with Li vacancies (LV phases) of a few micrometers or less in sizes formed in the LiFePO4 (LFP) phase during delithiation at a low potential of 4 V vs Li/Li+, and LV phases migrated at a rate corresponding to Li diffusivity of 3 × 10–9 cm2/s. In contrast, at a high potential of 4.5 V, an FePO4 (FP) phase grew in addition to the LV phase, and the rates of growth of the FP phase and migration of LV phases were characterized by quite different Li diffusivities of 1.4 × 10–11 cm2/s and close to 10–7 cm2/s, respectively. T...

High-pressure optical floating-zone growth of Li(Mn,Fe)PO4 single crystals

Mm-sized LiMn1−xFexPO4 single crystals with 0⩽x⩽1 were grown by means of the traveling floating-zone technique at elevated Argon pressure of 30bar. For the various doping levels, the growth process was optimized with respect to the composition-dependant effective light absorption and transparency of the materials. A convex crystal/melt interface, determined by the angle of incident light, was identified to be particularly crucial for a successful growth. The resulting large single crystalline grains are stoichiometric. Structure refinement shows that lattice parameters as well as the atomic positions and bond lengths linearly depend on the Mn:Fe-ratio. Oriented cuboidal samples with several mm3 of volume were used for magnetic studies which imply an antiferromagnetic ground state for all compositions. The Néel-temperature changes from TN=32.5(5)K in LiMnPO4 to 49.5(5)K in LiFePO4 while the easy magnetic axis in the ordered phase flips from the crystallographic a- to the b-axis upon Fe-doping of x<0.2.

First-Principles Investigation of the 57Fe Mössbauer Parameters of LiFePO4 and FePO4

The 57Fe Mossbauer isomer shift and quadrupole splitting of LiFePO4 (LFP) and FePO4 (FP) were evaluated from density functional theory. The effects of structural optimization, Fe 3d electron correlation, and spin configuration are found to be rather small for the isomer shift but not for the quadrupole splitting. The observed decrease of the isomer shift from LFP to FP is explained from the variations of both Fe 4s and Fe 3d electrons and is related to differences in the Fe–O chemical bond properties caused by oxidation of high-spin Fe2+ into high-spin Fe3+. The values of the quadrupole splitting of the two compounds strongly increase from nonspin-polarized to spin-polarized calculations and then slightly increase by taking into account the Fe 3d electron correlation, providing a good agreement with experimental data. The observed decrease of the quadrupole splitting from LFP to FP is quantitatively correlated to the decrease of the magnitude of the highest principal value VZZ of the electric field gradie...

Important Variation in Vibrational Properties of LiFePO4 and FePO4 Induced by Magnetism.

A new thermodynamically self-consistent (TSC) method, based on the quasi-harmonic approximation (QHA), is used to obtain the Debye temperatures of LiFePO4 (LFP) and FePO4 (FP) from available experimental specific heat capacities for a wide temperature range. The calculated Debye temperatures show an interesting critical and peculiar behavior so that a steep increase in the Debye temperatures is observed by increasing the temperature. This critical behavior is fitted by the critical function and the adjusted critical temperatures are very close to the magnetic phase transition temperatures in LFP and FP. Hence, the critical behavior of the Debye temperatures is correlated with the magnetic phase transitions in these compounds. Our first-principle calculations support our conjecture that the change in electronic structures, i.e. electron density of state and electron localization function, and consequently the change in thermophysical properties due to the magnetic transition may be the reason for the observation of this peculiar behavior of the Debye temperatures.

Thermal Stability and Reactivity of Cathode Materials for Li-Ion Batteries.

The thermal stability of electrochemically delithiated Li0.1Ni0.8Co0.15Al0.05O2 (NCA), FePO4 (FP), Mn0.8Fe0.2PO4 (MFP), hydrothermally synthesized VOPO4, LiVOPO4, and electrochemically lithiated Li2VOPO4 is investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis, coupled with mass spectrometry (TGA-MS). The thermal stability of the delithiated materials is found to be in the order of NCA < VOPO4 < MFP < FP. Unlike the layered oxides and MFP, VOPO4 does not evolve O2 on heating. Thus, VOPO4 is less likely to cause a thermal run-away phenomenon in batteries at elevated temperature and so is inherently safer. The lithiated materials LiVOPO4, Li2VOPO4, and LiNi0.8Co0.15Al0.05O2 are found to be stable in the presence of electrolyte, but sealed-capsule high-pressure experiments show a phase transformation of VOPO4 → HVOPO4 → H2VOPO4 when VOPO4 reacts with electrolyte (1 M LiPF6 in EC/DMC = 1:1) between 200 and 300 °C. Using first-principles calculations, we confirm that the charged VOPO4 cathode is indeed predicted to be marginally less stable than FP but significantly more stable than NCA in the absence of electrolyte. An analysis of the reaction equilibria between VOPO4 and EC using a multicomponent phase diagram approach yields products and reaction enthalpies that are highly consistent with the experiment results.