Reactivity, stability and electrochemical behavior of lithium iron phosphates

Life Cycle of LiFePO4 Batteries: Production, Recycling, and Market Trends

Significant attention has focused on olivine-structured LiFePO4 (LFP) as a promising cathode active material (CAM) for lithium-ion batteries. This iron-based compound offers advantages over commonly used Co and Ni due to its lower toxicity abundance, and cost-effectiveness. Despite its current commercial use in energy storage technology, there remains a need for cost-effective production methods to create electrochemically active LiFePO4. Consequently, there is ongoing interest in developing innovative approaches for LiFePO4 production. While LFP batteries exhibit significant thermal stability, cycling performance, and environmental benefits, their growing adoption has increased battery disposal rates. Improper disposal practices for waste LFP batteries result in environmental degradation and the depletion of valuable resources. This review comprehensively examines diverse synthesis approaches for generating LFP powders, encompassing conventional methodologies alongside novel procedures. Furthermore, it conducts an in-depth assessment of the methodologies employed in recycling waste LFP batteries. Moreover, it emphasizes the importance of LFP cathode recycling and investigates pretreatment techniques to enhance understanding. Additionally, it provides valuable insights into the recycling process of used LFP batteries, aiming to raise awareness regarding the market for retired LFP batteries and advocate for the enduring sustainability of lithium-ion batteries.

Many-Particle Li Ion Dynamics in LiMPO4 Olivine Phosphates (M = Mn, Fe)

LiMPO₄ (M = Mn, Fe) olivine phosphates are important materials for battery applications due to their stability, safety, and reliable recharge cycle. Despite continuous experimental and computational investigations, several aspects of these materials remain challenging, including conductivity dimensionality and how it maps onto Li pathways. In this work, we use a refined version of our finite temperature molecular dynamics "shooting" approach, originally designed to enhance Li hopping probability. We perform a comparative analysis of ion mobility in both materials, focused on many-particle effects. Therein, we identify main [010] diffusion channels, as well as means of interchannel couplings, in the form of Li lateral [001] hopping, which markedly impact the overall mobility efficiency as measured by self-diffusion coefficients. This clearly supports the need of many-particle approaches for reliable mechanistic investigations and for battery materials benchmarking due to the complex nature of the diffusion and transport mechanisms.

Mesoporous Polyimide-Linked Covalent Organic Framework with Multiple Redox-Active Sites for High-Performance Cathodic Li Storage

Covalent organic frameworks (COFs) are gaining increasing attention as renewable cathode materials for Li-ion batteries. However, COF electrodes reported so far still exhibit unsatisfying capacity due to their limited active site density and insufficient utilization. Herein, a new two-dimensional polyimide-linked COF, HATN-AQ-COF with multiple redox-active sites for storing Li⁺ ions, was designed and fabricated from a new module of 2,3,8,9,14,15-hexacarboxyl hexaazatrinaphthalene trianhydrides with a 2,6-diaminoanthraquinone linker. HATN-AQ-COF possessing excellent stability, good conductivity, and a large pore size of 3.8 nm enables the stable and fast ion transport. This, in combination with the abundant redox active sites, results in a high reversible capacity of 319 mAh g^-1 at 0.5 C (1 C=358 mA g^-1 ) for the HATN-AQ-COF electrode with a high active site utilization of 89 % and good cycle performance, representing one of the best performances among the reported COF electrodes.

Large-Scale Li-Ion Battery Research and Application in Mining Industry

The lithium-ion battery (LIB) has the advantages of high energy density, low self-discharge rate, long cycle life, fast charging rate and low maintenance costs. It is one of the most widely used chemical energy storage devices at present. However, the safety of LIB is the main factor that restricts its commercial scalable application, specifically in hazardous environments such as underground coal mines. When a LIB is operating under mechanical and electrical abuse such as extrusion, impact, overcharge and overheating, it will trigger thermal runaway and subsequently cause fire or even an explosion. According to the relevant requirements in IEC60079, the explosion-proof protection of LIB can be adapted to the working environment of high dust and explosive gas environments such as in the mining face of coal production. This paper presents an overview of the LIB-relevant technology, thermal runaway, safety and applications in the general mining industry with implications to establish a theoretical and technical basis for the application of high-capacity LIBs in the industry. These then promote intelligent, safe and efficient production not only for the coal mine industry but also for non-coal applications.

An overview of hydroxy-based polyanionic cathode insertion materials for metal-ion batteries

Rechargeable batteries based on Li-ion and post Li-ion chemistry have come a long way since their inception in the early 1980s. The last four decades have witnessed steady development and discovery of myriads of cathode materials taking into account their processing, economy, and performance along with ecological sustainability. Though oxides rule the battery sector with their high energy and power density, polyanionic insertion compounds work as gold mines for designing insertion compounds with rich structural diversity leading to tuneable redox potential coupled with high structural/chemical/thermal stability. The scope of polyanionic compounds can be taken a step further by combining two or more different types of polyanions to get suites of mixed polyanionic materials. While most cathodes are built with metal polyhedra constituted by oxygen (MO_m|XO_m, M = 3d metals, X = P, S, Si, B, W, etc., m = 3-6), in some cases, selected oxygen sites can form bonding with hydrogen to form OH/H₂O ligands. It can lead to the family of hydroxy-based mixed-polyanionic cathode materials. The presence of hydroxy components can affect the crystal structure, local chemical bonding, and electronic, magnetic, diffusivity and electrochemical properties. Employing a mineralogical survey, the current review renders a sneak peek on various hydroxy-based polyanionic cathode materials for Li-ion and post Li-ion batteries. Their crystal structure, and electrochemical properties have been overviewed to outline future research focus and scope for real-life application.

Spark Plasma Sintering of LiFePO4: AC Field Suppressing Lithium Migration

Our work proposes a comparison between Spark Plasma Sintering of LiFePO₄ carried out using an Alternating Current (AC) and Direct Current (DC). It quantifies the Li-ion migration using DC, and it validates such hypothesis using impedance spectroscopy, X-ray photoelectron spectroscopy and inductively coupled plasma optical emission spectroscopy. The use of an AC field seems effective to inhibit undesired Li-ion migration and achieve high ionic conductivity as high as 4.5 × 10⁻³ S/cm, which exceeds by one order of magnitude samples processed under a DC field. These results anticipate the possibility of fabricating a high-performance all-solid-state Li-ion battery by preventing undesired Li loss during SPS processing.

Understanding the sodium ion transport properties, deintercalation mechanism, and phase evolution of a Na2Mn2Si2O7 cathode by atomistic simulation

Molecular dynamics (MD) together with the first principles method (DFT) reveal that Na+ is capable of migrating three dimensionally in a Na2Mn2Si2O7 cathode material. Migration along the a-axis and c-axis have the same mechanism, that is, alternating between the Na1 and Na2 route with a similar local environment and distance. Long-distance hopping between two Na2 atoms or between Na1 and Na2 atoms is crucial for continuous migration along the b-axis. Also, the anti-site phenomenon is identified, and it facilitates the migration of the Na ions. Four intermediate phases are determined according to the formation energy curve and, as a result, the voltage profile is predicted accurately. The state of charge (SOC) dependency of the Na+ energy shows that the mobility of Na+ is highly inhibited in the fully discharged state. Upon the deintercalation of sodium ions, Na+ is activated immediately. A maximal DNa+ value of 3.6 × 10-9 cm2 s-1 and a low energy barrier of ca. 0.26 eV at the deintercalation level of x = 0.25 are observed. Because of the scarcity of Na+, DNa+ experiences a sharp decrease at the end of deintercalation. Despite the low level of Na+ mobility in the range of 0.25 < x < 1, Na2Mn2Si2O7 is still a potential cathode material for use in sodium ion batteries (SIBs).

Effect of crystallite size on the phase transition behavior of heterosite FePO4

For advanced lithium-ion battery technology, olivine-based cathodes are considered to be the most dominant and technologically recognized materials. The extraction of lithium ions from olivine LiFePO₄ results in the two-phase mixture with heterosite FePO₄ exhibiting a deintercalation potential of 3.45 V vs. Li⁺/Li over a wide range of lithium content. Here, we report the synthesis and characterization of chemically deintercalated heterosite FePO₄ with varying crystallite sizes using different analytical techniques. The decrease in the crystallite size of heterosite FePO₄ leads to an increase in the lattice parameters including the unit cell volume. The characteristic behavior in the structural properties of heterosite FePO₄ shows a strong dependency on the crystallite size which is correlated with the change in the chemical bonding. The volume expansion of the nano-sized heterosite FePO₄ with respect to the bulk counterpart is suggested to be a direct consequence of reduced hybridization between the Fe3d and O2p states. Furthermore, the combined X-ray diffraction and Mössbauer spectroscopic studies reveal the appearance of a new phase namely trigonal FePO₄ at the lower crystallite sizes due to the enhanced surface energy kinetics. We also find that the observed trigonal FePO₄ phase is more magnetically active than the paramagnetic olivine FePO₄. For the unique structural advantage of the heterosite phase as an electrode material, the change in bonding characteristics is very useful and can have strong implications on the electronic properties of heterosite FePO₄ at the nanoscale level.

Revisiting Electrochemical Techniques to Characterize the Solid-State Diffusion Mechanism in Lithium-Ion Batteries

Lithium-ion batteries (LiBs) have gained a worldwide position as energy storage devices due to their high energy density, power density and cycle life. Nevertheless, these performance parameters are yet insufficient for current and future demands diversifying their range of applications, and competitiveness against other power sources. In line with the materials science, the optimization of LiBs, first, requires an in-depth characterization and understanding of their determining steps regarding transport phenomena and electrode kinetics occurring within these devices. Experimental and theoretical studies have identified the solid-state diffusion of Li+into the composite cathode material as one of the transport mechanisms limiting the performance of LiBs, in particular at high charge and discharge rates (C-rates). Nowadays, there is however ambivalence to characterize this mass transport mechanism using the diffusion coefficient calculated either by electrochemical techniques orab initioquantum chemistry methods.  This contribution revisits conventional electrochemical methodologies employed in literature to estimate mass transport diffusivity of LiBs, in particular using LiFePO4in the cathode, and their suitability and reliability are comprehensively discussed. These experimental and theoretical methods include Galvanostatic and Potentiostatic Intermittent Titration Technique (GITT and PITT), Electrochemical Impedance Spectroscopy (EIS), Cyclic Voltammetry (CV) andab initioquantum chemistry methods. On the one hand, experimental methods seem not to isolate the diffusion mechanism in the solid phase; thus, obtaining an unreliable apparent diffusion coefficient (ranging from 10–10to 10–16 cm2 s−1), which only serves as a criterion to discard among a set of LiBs. On the other hand, atomistic approaches based onab initio, density functional theory (DFT), cannot yet capture the complexity of the local environments involved at this scale; in consequence, these approaches have predicted inadequate diffusion coefficients for LiFePO4(ranging from 10–6to 10–7 cm2 s−1) which strongly differ from experimental values. This contribution, at long last, remarks the factors influencing diffusion mechanisms and addresses the uncertainties to characterize this transport mechanism in the cathode, stressing the needs to establish methods to determine the diffusion coefficient accurately, coupling electrochemical techniques,ab initiomethods, and engineering approaches based on modeling.

Defect physics in complex energy materials

Understanding the physics of structurally and chemically complex transition-metal oxide and polyanionic materials such as those used for battery electrodes is challenging, even at the level of pristine compounds. Yet these materials are also prone to and their properties and performance are strongly affected or even determined by crystallographic point defects. In this review, we highlight recent advances in the study of defects and doping in such materials using first-principles calculations. The emphasis is on describing a theoretical and computational approach that has the ability to predict defect landscapes under various synthesis conditions, provide guidelines for defect characterization and defect-controlled synthesis, uncover the mechanisms for electronic and ionic conduction and electrochemical extraction and (re-)insertion, and provide an understanding of the effects of doping. Though applied to battery materials here, the approach is general and applicable to any materials in which the defect physics plays a role or drives the properties of interest. Thus, this work is intended as an in-depth review of defect physics in particular classes of materials, but also as a methodological template for the understanding and design of complex functional materials.

Two-dimensional lithium diffusion behavior and probable hybrid phase transformation kinetics in olivine lithium iron phosphate

Olivine lithium iron phosphate is a technologically important electrode material for lithium-ion batteries and a model system for studying electrochemically driven phase transformations. Despite extensive studies, many aspects of the phase transformation and lithium transport in this material are still not well understood. Here we combine operando hard X-ray spectroscopic imaging and phase-field modeling to elucidate the delithiation dynamics of single-crystal lithium iron phosphate microrods with long-axis along the [010] direction. Lithium diffusivity is found to be two-dimensional in microsized particles containing ~3% lithium-iron anti-site defects. Our study provides direct evidence for the previously predicted surface reaction-limited phase-boundary migration mechanism and the potential operation of a hybrid mode of phase growth, in which phase-boundary movement is controlled by surface reaction or lithium diffusion in different crystallographic directions. These findings uncover the rich phase-transformation behaviors in lithium iron phosphate and intercalation compounds in general and can help guide the design of better electrodes.

Lithium transport and phase transformation kinetics in olivine LiFePO₄ electrode remain not fully understood. Here the authors show that microsized olivine particles possess 2D lithium diffusivity and exhibit a possible hybrid mode of phase boundary migration upon cycling.

Quantitative description on structure-property relationships of Li-ion battery materials for high-throughput computations

Li-ion batteries are a key technology for addressing the global challenge of clean renewable energy and environment pollution. Their contemporary applications, for portable electronic devices, electric vehicles, and large-scale power grids, stimulate the development of high-performance battery materials with high energy density, high power, good safety, and long lifetime. High-throughput calculations provide a practical strategy to discover new battery materials and optimize currently known material performances. Most cathode materials screened by the previous high-throughput calculations cannot meet the requirement of practical applications because only capacity, voltage and volume change of bulk were considered. It is important to include more structure-property relationships, such as point defects, surface and interface, doping and metal-mixture and nanosize effects, in high-throughput calculations. In this review, we established quantitative description of structure-property relationships in Li-ion battery materials by the intrinsic bulk parameters, which can be applied in future high-throughput calculations to screen Li-ion battery materials. Based on these parameterized structure-property relationships, a possible high-throughput computational screening flow path is proposed to obtain high-performance battery materials.

Crystal chemistry of Mg substitution in NaMnPO4olivine: concentration limit and cation distribution

In Mg-substituted NaMnPO₄, Na⁺, Mg²⁺and metal vacancies reside in the M1 olivine position, while Mn²⁺ions are predominantly in the M2 position.

Non-stoichiometric carbon-coated LiFexPO4as cathode materials for high-performance Li-ion batteries

This work first discloses the evolution of lattice parameters of the non-stoichiometric lithium iron phosphate crystals.

One-Dimensional Peptide Nanostructure Templated Growth of Iron Phosphate Nanostructures for Lithium-Ion Battery Cathodes

Template-directed synthesis of nanomaterials can provide benefits such as small crystalline size, high surface area, large surface-to-volume ratio, and structural stability. These properties are important for shorter distance in ion/electron movement and better electrode surface/electrolyte contact for energy storage applications. Here nanostructured FePO4 cathode materials were synthesized by using peptide nanostructures as a template inspired by biomineralization process. The amorphous, high surface area FePO4 nanostructures were utilized as a cathode for lithium-ion batteries. Discharge capacity of 155 mAh/g was achieved at C/20 current rate. The superior properties of biotemplated and nanostructured amorphous FePO4 are shown compared to template-free crystalline FePO4.

Accelerated Removal of Fe-Antisite Defects while Nanosizing Hydrothermal LiFePO4 with Ca(2)

Based on neutron powder diffraction (NPD) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), we show that calcium ions help eliminate the Fe-antisite defects by controlling the nucleation and evolution of the LiFePO4 particles during their hydrothermal synthesis. This Ca-regulated formation of LiFePO4 particles has an overwhelming impact on the removal of their iron antisite defects during the subsequent carbon-coating step since (i) almost all the Fe-antisite defects aggregate at the surface of the LiFePO4 crystal when the crystals are small enough and (ii) the concomitant increase of the surface area, which further exposes the Fe-antisite defects. Our results not only justify a low-cost, efficient and reliable hydrothermal synthesis method for LiFePO4 but also provide a promising alternative viewpoint on the mechanism controlling the nanosizing of LiFePO4, which leads to improved electrochemical performances.

Synthesis, characterisation and enhanced electrochemical performance of nanostructured Na2FePO4F for sodium batteries

Nanostructured Na₂FePO₄F was synthesised by a soft template method, followed by high-energy ball milling (HEBM) and post-heat treatment. The HEBM sample shows excellent sodium storage performance with a discharge capacity of 116 mA h g⁻¹at 0.1 C.

Materials for suspension (semi-solid) electrodes for energy and water technologies

Conducting suspension electrodes for novel flow-assisted electrochemical systems such as grid energy storage, water deionization, and water treatment.

Large-scale preparation of Mg doped LiFePO4@C for lithium ion batteries via carbon thermal reduction combined with aqueous rheological phase technology

A uniform distribution of doped metal and coated carbon in the as-prepared LiFePO₄material is obtained. The LiFePO₄delivers a discharge capacity of 166 mA h g⁻¹at 0.1C and presents excellent rate capacity and a high potential plateau at 1C.

Tailored surface structure of LiFePO4/C nanofibers by phosphidation and their electrochemical superiority for lithium rechargeable batteries

We offer a brand new strategy for enhancing Li ion transport at the surface of LiFePO4/C nanofibers through noble Li ion conducting pathways built along reduced carbon webs by phosphorus. Pristine LiFePO4/C nanofibers composed of 1-dimensional (1D) LiFePO4 nanofibers with thick carbon coating layers on the surfaces of the nanofibers were prepared by the electrospinning technique. These dense and thick carbon layers prevented not only electrolyte penetration into the inner LiFePO4 nanofibers but also facile Li ion transport at the electrode/electrolyte interface. In contrast, the existing strong interactions between the carbon and oxygen atoms on the surface of the pristine LiFePO4/C nanofibers were weakened or partly broken by the adhesion of phosphorus, thereby improving Li ion migration through the thick carbon layers on the surfaces of the LiFePO4 nanofibers. As a result, the phosphidated LiFePO4/C nanofibers have a higher initial discharge capacity and a greatly improved rate capability when compared with pristine LiFePO4/C nanofibers. Our findings of high Li ion transport induced by phosphidation can be widely applied to other carbon-coated electrode materials.

Morphological and orientational diversity of LiFePO4crystallites: remarkable reaction path dependence in hydrothermal/solvothermal syntheses

Reaction path difference in synthesis conditions has resulted in the morphological and orientational diversity of resultant LiFePO₄crystallites.

Effect of PPy/PEG conducting polymer film on electrochemical performance of LiFePO4 cathode material for Li-ion batteries

Rechargeable lithium-ion batteries (LIBs) have been the most commonly used batteries in the portable electronics market for many years. Polypyrrole (PPy) was now investigated as a conducting addition agent to enhance the cathode and anode materials performance in LIBs. Actual development in the synthesis and modification of the most promising cathode materials, LiFePO4, is described in this mini-review. The main aim of this mini-review is to highlight the effect of PPy based conducting polymer films on the electrochemical efficiency of LiFePO4 based cathode materials for LIBs summarizing our own research. Influence of the polyethylene glycol (PEG) additive in the PPy coating layer was evaluated. The improved electrochemical performance can be attributed to the enhanced electronic conductivity, higher solubility of ions originating from the electrolyte, higher movability of dissolved Li+ ions, and improved structural flexibility resulting from the incorporation of the PPy or PPy/PEG conducting polymer layer. The stabilizing effect of PEG in PPy was reflected in lowered cross-linking and reduced structural defects and, in consequence, in higher specific capacity of PPy/PEG-LiFePO4 cathodes compared to that of PPy-LiFePO4 cathodes and bare LiFePO4 cathodes.

Vacancy-driven anisotropic defect distribution in the battery-cathode material LiFePO4

Li-ion mobility in LiFePO(4), a key property for energy applications, is impeded by Fe antisite defects (Fe(Li)) that form in select b-axis channels. Here we combine first-principles calculations, statistical mechanics, and scanning transmission electron microscopy to identify the origin of the effect: Li vacancies (V(Li)) are confined in one-dimensional b-axis channels, shuttling between neighboring Fe(Li). Segregation in select channels results in shorter Fe(Li)-Fe(Li) spans, whereby the energy is lowered by the V(Li)'s spending more time bound to end-point Fe(Li)'s. V(Li)-Fe(Li)-V(Li) complexes also form, accounting for observed electron energy loss spectroscopy features.