PO4 Cathode Research Articles

Promoting All Key Parameters of LiFe0.5Mn0.5PO4 Cathodes with Monovalent Ag+ Doping: A Smart Two-Birds-with-One-Stone Strategy

Promoting All Key Parameters of LiFe0.5Mn0.5PO4 Cathodes with Monovalent Ag+ Doping: A Smart Two-Birds-with-One-Stone Strategy

A Uniform Conductive Carbon Coating of Nitrogen‐Doped Carbon Improves the Electrochemical Performance of LiMn0.7Fe0.3PO4 Cathode Material for Lithium‐ion Batteries

AbstractThe practical application of LiMn1−xFexPO4 as a cathode material is hindered considerably by its poor electronic conductivity and slow lithium‐ion diffusion. In the present study, a uniform nitrogen‐doped carbon coating on LiMn0.7Fe0.3PO4 (LiMn0.7Fe0.3PO4@NC) was achieved using ethylene diamine tetraacetic acid (EDTA) as a chelating agent and carbon source. The nitrogen‐doped carbon layer enhanced the electronic conductivity and ionic diffusion of the LiMn0.7Fe0.3PO4 cathode. Furthermore, the uniform carbon layer prevented metal ion dissolution and stabilized the crystal structure. The resulting LiMn0.7Fe0.3PO4@NC‐2 sample demonstrated superior performance with a specific capacity of 152.5 mAh g−1 at 0.1 C and preserved 93.7 % of this capacity over 200 cycles at 1 C. Meanwhile, the LiMn0.7Fe0.3PO4@NC‐2 sample demonstrated a high Li+ diffusion coefficient (3.98×10−11 cm2 s−1) and electrical conductivity (1.47×10−2 S cm−1). This study presents a novel approach to designing high‐performance cathode materials using a cost‐effective and straightforward process.

Modulating the lattice structure via Cr3+ doping in LiFe0.4Mn0.6PO4 cathode for improved rate behavior and promoted cyclic performance

Although LiFe0.4Mn0.6PO4 cathode shows high potential in battery industry, the cyclic performance and rate behavior are still the concerns to overcome. In this paper, Cr3+ doping in the cathode is confirmed very effective to improve both the performance via increased Li migration kinetics and suppressed lattice expansion during the redox process. It is found from the XRD refinement that Li − O bond length is increased upon Cr3+ intercalation, which in turn leads to the decrease in migration energy barrier (from 48.41 KJ·mol−1 to 19.57 KJ·mol−1) and the increase in Li diffusion coefficient. GITT investigation reveals a big promotion of DLi from 7.38 × 10−11 cm2·s−1 to 4.47 × 10−10 cm2·s−1, which is regarded as the reason for the excellent rate capacity of 126.62 mAh·g−1 (80.8 % of the value at 0.1C) at 5C current density. Further study with ex-situ XRD investigation reveals that the lattice expansion during redox process is suppressed after Cr3+ doping due to the smaller radius and stronger bond energy of the substituted cations. The suppressed volume change decreases both the internal resistance and the polarization of the electrode, which therefore leads to an improved capacity retention. The initial discharge specific capacity of LFMP-2%Cr cathode material reaches 156.8 mAh·g−1 at 0.1C, and the capacity retention rate of the material is maintained as 98.4 % after 100 cycles at 0.5C. The above results reveal the effectiveness of Cr3+ in promoting the electrochemical performance and further confirm the Cr- doped LFMP cathode high potential in future application.

Electrochemically induced interface by LiBOB to enhance cycling performance of LiFe0.4Mn0.6PO4 cathode for lithium-ion batteries

Olivine-type lithium iron manganese phosphate (LFMP) combines the high energy density of LiMnPO4 with the high safety of LiFePO4, is considered to be one of the most promising cathode materials for the next generation. However, the Mn dissolution behavior due to the Jahn-Teller effect of Mn3+ irreversibly causes loss of active material during electrochemical cycling, accompanied by severe capacity decay and structural degradation, which is more severe at elevated temperature. Herein, in order to enhance the cycling performance of LFMP cathode material, the cathode-electrolyte interface is stabilized by inducing bis(oxalate)borate (LiBOB) decomposition electrochemically to form a CEI layer. Specifically, the capacity retention of the battery in the electrolyte containing 0.75 wt% LiBOB is 95.37 % after 200 cycles at 25 °C and 1C. (1C = 170 mA g−1) The capacity retention is 89.17 % after 200 cycles at 55 °C and 1C, compared to only 72 % in the electrolyte without LiBOB. The superior cycling performance is attributed to the formation of a uniform CEI layer induced by LiBOB electrochemically, which inhibits the parasitic reaction between the cathode and electrolyte, reduces the dissolution of Mn in the active substance, enabling superior and safer cycling performance even at elevated temperature.

Effects of liquid-phase carbon combining surfactant coatings on the performance of LiMn0.2Fe0.8PO4 cathode materials

Efforts to reduce the particle size of LiFexMn1-xPO4 materials and apply conductive carbon coatings have yielded substantial benefits in terms of obtaining lithium-ion batteries (LIBs) with enhanced electrochemical performance. However, LiFexMn1-xPO4 materials with small particle sizes and uniform carbon layers cannot be obtained by the conventional high-temperature solid-phase method, which is the most convenient and applicable method for the industrial-scale preparation of the cathode materials used in commercial LIBs. The present work addresses this issue by applying the cationic surfactant cetyltrimethylammonium bromide (CTAB) in conjunction with LiMn0.2Fe0.8PO4 (LMFP) particles, and obtaining a carbon layer by replacing the conventional in-situ solid-phase carbon coating process with a secondary liquid-phase coating process using sucrose as the carbon source. The CTAB surfactant is observed to be uniformly adsorbed on the surface of LMFP particles, and maintains small LMFP particle sizes by operating as a dispersant preventing their agglomeration. Additionally, the carbon network formed by CTAB pyrolysis acts as an intermediate medium ensuring that the conductive carbon layer is uniformly and firmly adhered to the LMFP particle surfaces at a high preparation temperature of 680°C. This composite carbon layer is demonstrated to enhance lithium-ion transport, while concurrently acting as a barrier interfering with manganese diffusion within the electrolyte during charge-discharge cycling. As a result, the optimal LMFP-based cathode material achieves reversible specific capacities of 160 mAh g−1 and 120 mAh g−1 at charge-discharge rates of 0.1 C and 5 C, respectively, and the capacity retention is 88 % after 500 cycles at 1 C. Hence, the results verify that the proposed surfactant-mediated liquid-phase carbon coating process is an effective method for enhancing the overall electrochemical performance of LMFP-based cathode materials.

Na/Co dual-doped olivine LiMn0.6Fe0.4PO4 cathode with superior reaction kinetics for Li-ion batteries

Na/Co dual-doped olivine LiMn0.6Fe0.4PO4 cathode with superior reaction kinetics for Li-ion batteries

The Effect of Oxygen Vacancy Defects on the Structure and Electrochemical Behaviors of LiMn0.65Fe0.35PO4 Cathode

The presence of oxygen vacancy defects significantly impacts the crystal structure and electrochemical attributes of phosphate cathodes. In this investigation, LiMn0.65Fe0.35PO4 materials with varying levels of oxygen vacancy defects were synthesized via hydrogen plasma-induced reduction. It was observed that the content of oxygen vacancy defects on the crystal surface increased proportionately with the rise in hydrogen (H2) flow rate. Notably, the LMFP-3 sample, prepared with an H2 flow rate of 10 ml min−1, demonstrated superior electrochemical performance, characterized by a 159.7 mAh g−1 discharge capacity at 0.1 C and a remarkable 99.8% capacity retention at 5 C after 200 cycles. This enhancement in electrochemical performance is attributed to the improved intrinsic conductivity of the LiMn0.65Fe0.35PO4 material due to the presence of oxygen vacancy defects. However, it is important to note that an excessively high H2 flow rate can lead to the formation of Fe2P impurities, which hinder lithium ion (Li+) diffusion. Furthermore, theoretical calculations conducted using density functional theory provide a rational explanation for the observed improvement in electronic conductivity. The introduction of oxygen vacancy defects results in a significant reduction in the Band gap, which is highly beneficial for enhancing the intrinsic conductivity of the LiMn0.65Fe0.35PO4 materials.

A Dual-Bond Crosslinking Strategy Enabling Resilient and Recyclable Electrolyte Elastomers for Solid-State Lithium Metal Batteries.

Elastomeric solid polymer electrolytes (SPEs) are highly promising to address the solid-solid-interface issues of solid-state lithium metal batteries (LMBs), but compromises have to be made to balance the intrinsic trade-offs among their conductive, resilient and recyclable properties. Here, we propose a dual-bond crosslinking strategy for SPEs to realize simultaneously high ionic conductivity, elastic resilience and recyclability. An elastomeric SPE is therefore designed with hemiaminal dynamic covalent networks and Li+-dissociation co-polymer chains, where the -C-N- bond maintains the load-bearing covalent network under stress but is chemically reversible through a non-spontaneous reaction, the weaker intramolecular hydrogen bond is mechanically reversible, and the soft chains endow the rapid ion conduction. With this delicate structure, the optimized SPE elastomer achieves high elastic resilience without loading-unloading hysteresis, outstanding ionic conductivity of 0.2 mS cm-1 (25 °C) and chemical recyclability. Then, exceptional room-temperature performances are obtained for repeated Li plating/stripping tests, and stable cycling of LMBs with either LiFePO4 or 4.3 V-class LiFe0.2Mn0.8PO4 cathode. Furthermore, the recycled and reprocessed SPEs can be circularly reused in LMBs without significant performance degradation. Our findings provide an inspiring design principle for SPEs to address the solid-solid-interface and sustainability challenges of solid-state LMBs.

Providing high stability to suppress metal dissolution in LiMn0.5Fe0.5PO4 cathode materials by Zn doping

LiMnxFe1-xPO4 (LMFP) is a promising cathode material for Li-ion batteries owing to its higher energy density than that of LiFePO4. However, the Jahn-Teller distortion caused by Mn3+ and oxidation of Fe2+ leading electrolyte decomposition lowers its cycling performance and structure stability. To address these problems, this study proposes an optimized Zn-doping content to enhance the electrochemical performance of LMFP. Results indicate that doping with 1.0 % Zn (LMFP-Zn 1.0 %) achieves the optimal cycling performance. Especially, LMFP-Zn 1.0 % exhibits 92.6 % capacity retention after 100 cycles at 2C. The HR-TEM and XPS analyses confirm that this level of doping suppresses metal dissolution and structure destruction effectively after cycling at high C-rates, resulted in improving the electrochemical performance and stability of LMFP cathode materials.

A Dual‐Bond Crosslinking Strategy Enabling Resilient and Recyclable Electrolyte Elastomers for Solid‐State Lithium Metal Batteries

Elastomeric solid polymer electrolytes (SPEs) are highly promising to address the solid‐solid‐interface issues of solid‐state lithium metal batteries (LMBs), but compromises have to be made to balance the intrinsic trade‐offs among their conductive, resilient and recyclable properties. Here, we propose a dual‐bond crosslinking strategy for SPEs to realize simultaneously high ionic conductivity, elastic resilience and recyclability. An elastomeric SPE is therefore designed with hemiaminal dynamic covalent networks and Li+‐dissociation co‐polymer chains, where the ‐C‐N‐ bond maintains the load‐bearing covalent network under stress but is chemically reversible through a non‐spontaneous reaction, the weaker intramolecular hydrogen bond is mechanically reversible to dissipate elastic energy, and the soft chains endow the rapid ion conduction. With this delicate structure, the optimized SPE elastomer achieves high elastic resilience without loading‐unloading hysteresis, outstanding ionic conductivity of 0.2 mS cm‐1 (25 °C) and chemical recyclability. Then, exceptional room‐temperature performances are obtained for repeated Li plating/stripping tests, and stable cycling of LMBs with either LiFePO4 or 4.3 V‐class LiFe0.2Mn0.8PO4 cathode. Furthermore, the recycled SPE can be circularly reused in LMBs without significant performance degradation. Our findings provide an inspiring design principle for SPEs to address the solid‐solid‐interface and sustainability challenges of solid‐state LMBs.

Unravelling the ion transport and the interphase properties of a mixed olivine cathode for Na-ion battery

The replacement of Li by Na in an analogue battery to the commercial Li-ion one appears a sustainable strategy to overcome the several concerns triggered by the increased demand for the electrochemical energy storage. However, the apparently simple change of the alkali metal represents a challenging step which requires notable and dedicated studies. Therefore, we investigate herein the features of a NaFe0.6Mn0.4PO4 (NFMP) cathode with triphylite structure achieved from the conversion of a LiFe0.6Mn0.4PO4 (LFMP) olivine for application in Na-ion battery. The work initially characterizes the structure, morphology and performances in sodium cell of NFMP, achieving a maximum capacity exceeding 100 mAh g−1 at a temperature of 55 °C, adequate rate capability, and suitable retention confirmed by ex-situ measurements. Subsequently, the study compares in parallel key parameters of the NFMP and LFMP such as Na+/Li+ ions diffusion, interfacial characteristics, and reaction mechanism in Na/Li cells using various electrochemical techniques. The data reveal that relatively limited modifications of NFMP chemistry, structure and morphology compared to LFMP greatly impact the reaction mechanism, kinetics and electrochemical features. These changes are ascribed to the different physical and chemical features of the two compounds, the slower mobility of Na+ with respect to Li+, and a more resistive electrode/electrolyte interphase of sodium compared with lithium. Relevantly, the study reveals analogue trends of the charge transfer resistance and the ion diffusion coefficient in NFMP and LFMP during the electrochemical process in half-cell. Hence, the NFMP achieved herein is suggested as a possible candidate for application in a low-cost, efficient, and environmentally friendly Na-ion battery.

Boosting both electronic and ionic conductivities via incorporation of molybdenum for LiFe0.5Mn0.5PO4 cathode in lithium-ion batteries

As the EV and ESS markets expand, there is a growing interest in LiFexMn1-xPO4 (LFMP) cathode materials amidst the increasing demand for LIBs. The LFMP cathode material is cost-effective and structurally stable; however, it has the drawback of low conductivity. Therefore, the development of an LFMP cathode material with high ionic/electronic conductivity is essential for high-stability and high-C-rate LIB applications. We propose a carbon-coated LFMP cathode material with Mo placed at the Fe and Mn sites. The samples were synthesized using a solvothermal method. Mo contributes to enhanced Li-ion diffusion and charge transfer rates. The XRD Rietveld refinement results showed elongated Li–O bonds within the Mo-doped LFMP/C, which accelerated the Li+ ion diffusion. Through SEM, TEM–EDS mapping, and XPS analysis we have confirmed the properties and morphology of the material. The electrochemical evaluation of the material was conducted using galvanostatic charge-discharge, CV, and EIS methods. Based on these tests, Mo incorporation not only increased the capacity but also enhanced the rate performance, reduced the voltage polarization, and improved the lithium-ion diffusion coefficient. Based on the 3.7 V additional plateau, which is attributed to the sluggish kinetics of Mn3+, Mo6+ played a role in enhancing the kinetic behavior of Mn3+. Low-temperature performance tests demonstrated that the Mo-doped samples exhibited high energy density, cycle retention, and superior ionic conductivity. In summary, an appropriate amount of Mo doping is effective for improving the electrochemical performance of LFMP, making it a promising cathode material.

Freeze-Drying-Assisted Preparation of High-Compaction-Density LiMn0.69Co0.01Fe0.3PO4 Cathode Materials with High-Capacity and Long Life-Cycle for Lithium Ion Batteries

As a successor to LiFePO4, the research interest in LiMn1−yFeyPO4 has been sustained due to its higher working voltage and safety features. However, its further application is limited by the low compaction density caused by uncontrolled particle size. In this study, the high-quality LiMn0.69Co0.01Fe0.3PO4 (LMFP) materials were prepared using the freeze-drying method to process the LMFP precursor synthesized through a solvothermal crystallization method followed by a calcination process at different temperatures (400–550 °C). The results demonstrate that the obtained particles exhibit a spheroidal shape with a low specific surface area after secondary crystallization calcination at 700 °C. The compaction density increased from 1.96 g/cm3 for LMFP precursor (LMFP-M1) to 2.18, 2.27, 2.34, and 2.43 g/cm3 for samples calcined at 400, 450, 500 and 550 °C, respectively, achieving a maximum increase of 24%. The full cell constructed with the high-compaction-density material calcined at 500 °C displayed discharge capacities of 144.1, 143.8, and 142.6 mAh/g at 0.5, 1, and 3 C rates, respectively, with a retention rate of 99% at 3 C rate. After undergoing charging and discharging cycles at a rate of 1 C for up to 800 cycles, the capacity retention rate was found to be 90%, indicating an expected full cell life span exceeding 2500 cycles.

Synthesis and Electrochemical Properties of Molybdenum-Doped LiMn0.6Fe0.4PO4 Cathode Materials

Synthesis and Electrochemical Properties of Molybdenum-Doped LiMn0.6Fe0.4PO4 Cathode Materials

Scalable, low-cost synthesis of high volumetric capacity LiMn0.5Fe0.5PO4 cathode for lithium-ion batteries

A facile, scalable, wastewater-free synthesis of high energy density LiMn0.5Fe0.5PO4 (LMFP) cathodes with high electrode press density is achieved by employing the spinel LiMnFeO4 (LMFO) as a precursor.

Relaxing the Jahn–Teller distortion of LiMn0.6Fe0.4PO4 cathodes via Mg/Ni dual-doping for high-rate and long-life Li-ion batteries

The synergistic doping of divalent Mg2+ and Ni2+ ions into a carbon-coated LiMn0.6Fe0.4PO4 cathode significantly enhances reaction kinetics and structural stability by mitigating the Jahn–Teller effect and accelerating the Li-ion migration rate.

Superior electronic/ionic kinetics of LiMn0.8Fe0.2PO4@C nanoparticles cathode by doping strategy toward enhanced Li-ion storage

The practical applications of LiMn0.8Fe0.2PO4 have been greatly limited due to its low electrical conductivity and inferior electrochemical reaction kinetics. Herein, a Ni-doped strategy has been employed to optimize the morphology of LiMn0.8Fe0.2PO4 nanoparticles with preferred growth orientation, leads to improved electrical/ionic conductivity and electrode kinetic. Compared with pristine sample (Ni-D0), the electrical conductivity, ion diffusion coefficient and exchange current density of 5 mol% Ni-doped sample (Ni-D5) are obviously increased to 9.57 × 10−2 S cm−1, 3.301 × 10−11 cm2 s−1, and 0.339 mA cm−2, respectively. The first principle calculations also confirmed the enhanced electrical conductivity of LiMn0.8Fe0.15Ni0.05PO4@C. Meanwhile, Ni-D5 exhibits good rate capability and cycling stability. Furthermore, the operando XRD analysis demonstrated its highly structural stability and reversible properties. Therefore, the Ni-doped strategy is considered a promising and effective modification approach to enhance the Li-storage capability of LiMn0.8Fe0.2PO4 cathode for high performance rechargeable second batteries.

Direct Upcycling of Leached FePO4 from Spent Lithium‐Ion Batteries toward Gradient‐Doped LiMnxFe1−xPO4 Cathode Material

AbstractLithium‐ion batteries (LIBs) with LiFePO4 (LFP) cathode materials have occupied a significant market share in state‐of‐the‐art power storage systems and electric vehicles, yet the approaching “retiring wave” of these LIBs should be appropriately treated (i.e., recycling of spent LIBs). Current recycling strategies of degraded LFP materials largely direct on leaching of lithium elements, leaving the leached FePO4 residual as a waste. Inspiringly, LiMnxFe1−xPO4 material is considered one of the potential candidates for next‐generation cathode materials because of its high electrochemical performance, extraordinary stability, and low cost. Herein, the direct upcycling of leached FePO4 toward LiMn0.25Fe0.75PO4 (LMFP) cathode material is demonstrated via a green, simple, and scalable mechanochemical pathway. The product features a gradient‐doping of Mn, as well as a uniform carbon coating for LMFP particles. As a result, the LMFP cathode material delivers superior electrochemical performance; the capacity (161.3 mA h g−1 at 0.1 C), rate capability (90.1 mA h g−1 at 5 C), cycling stability (95.6% capacity retention after 800 cycles at 1 C), and energy density (≈15% increase as compared to LFP) are almost comparable with those of fresh materials. The as‐established upcycling protocol offers a favorable reuse method for leached FePO4 materials.

Toxic solvent-free low-temperature fabrication and electrochemical performance of LiTa2PO8 ceramic matrix–based composite solid electrolytes containing polyvinylidene fluoride

Most studies of Composite solid electrolytes (CSEs) are composed of a polymer matrix and ceramic fillers. Polymer matrix–based CSEs are prepared by dissolving a polymer and lithium (Li) salt in a toxic organic solvent; then, a ceramic filler is added, and the toxic solvent is evaporated. These electrolytes contain 80%–90% polymer; however, they still have low thermal and electrochemical stability and unsatisfactory suppression of Li dendrite growth compared to inorganic ceramic electrolytes (ICEs). Ceramic matrix–based CSEs have high electrochemical and thermal stability, and good interfacial contact with electrodes. In this study, ceramic matrix–based CSEs were fabricated at a low temperature using a nontoxic solvent via the cold sintering process (CSP). Then, polyvinylidene fluoride (PVDF) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were introduced on the LiTa2PO8 (LTPO) particle interface. In addition, the effect of the ratio of LTPO–PVDF and PVDF–LiTFSI at the LTPO particle interface on the microstructure and electrochemical properties of composite pellets was investigated. LTPO–PVDF pellets exhibited a relative density of 82%–86%, and high adhesion between LTPO particles was observed due to the formation of PVDF–LiTFSI amorphous layer on the particle interface. The LTPO–PVDF composite pellets exhibited a high total ionic conductivity of 4.59 × 10−4 S/cm at room temperature (RT), negligible electronic conductivity of 3.89 × 10−8 S/cm, low activation energy of 0.259 eV, and sufficient electrochemical stability. Coin cells with LiMn0.6Fe0.4PO4 (LMFP) cathode exhibited a high initial discharge capacity of ∼145 mAh/g and capacity retention of approximately 85% after 50 cycles at RT. These results prove that the CSP is an ideal fabrication method for CSEs than the conventional methods that use toxic solvents and that introducing an amorphous layer at the particle interface in ceramic matrix–based CSEs improves their ionic conductivity.

Preparation of LiFe0.99Mn0.01PO4 Cathode Material with Lower Fe-Li Antisite via Wet-Lithiation Following by Tavorite-Olivine Phase Transition

Mn doping is widely used to improve the kinetic properties of LiFePO4 cathode materials. In this work, we synthesized LiFe0.99Mn0.01PO4 cathode material by a novel phase transition from the tavorite LiFePO4OH structure to the olivine LiFePO4 structure at 600 °C. A lower crystallization temperature not only results in a looser lattice for LiFePO4 material but also prevents crystal growth in higher temperatures and shortens the ion diffusion path. Experiments reveal that Mn doping can further broaden the lattice on this basis and thus ameliorate the Li+ diffusion property. The Density-Functional Theory (DFT) calculations not only support the above argument, but also predict that the LiFePO4 cathodes obtained from LiFePO4OH-to-LiFePO4 phase transition own lower Fe-Li antisite concentration (due to the high Fe-Li antisite formation energy of pre-lithiated precursor LiFePO4OH). As a result, the obtained LiFe0.99Mn0.01PO4 yields a discharge capacity close to the theoretical capacity of 169.2 mAh g−1 at a low rate of 0.2 C, 142.9 mAh g−1 at a high rate of 10 C and a capacity retention of 97.8% till 1000 cycles at 1 C. These findings indicate that the LiFePO4OH enabled by prelithiation in liquid provides a new idea for realizing substitution-modified LiFePO4 with optimal electrochemical performance.