Vanadium doping of LiMnPO4 cathode material: Correlation between changes in the material lattice and the enhancement of the electrochemical performance

A Promising Solid-State Synthesis of LiMn1- yFeyPO4 Cathode for Lithium-ion Batteries

LiMn1-yFeyPO4 (LMFP) is a significant and cost-effective cathode material for Li-ion batteries, with a higher working voltage than LiFePO4 (LFP) and improved safety features compared to layered oxide cathodes. However, its commercial application faces challenges due to a need for a synthesis process to overcome the low Li-ion diffusion kinetics and complex phase transitions. Herein, a solid-state synthesis process using LFP and nano LiMn0.7Fe0.3PO4 (MF73) is proposed. The larger LFP acts as a structural framework fused with nano-MF73, preserving the morphology and high performance of LFP. These results demonstrate that the solid-state reaction occurs quickly, even at a low sintering temperature of 500 °C, and completes at 700 °C. However, contrary to the expectations, the larger LFP particles disappeared and fused into the nano-MF73 particles, revealing that Fe ions diffuse more easily than Mn ions in the olivine framework. This discovery provides valuable insights into understanding ion diffusion in LMFP. Notably, the obtained LMFP can still deliver an initial capacity of 142.3 mAh g-1, and the phase separation during the electrochemical process is significantly suppressed, resulting in good cycling stability (91.1% capacity retention after 300 cycles). These findings offer a promising approach for synthesizing LMFP with improved performance and stability.

Simple synthesis of a hierarchical LiMn0.8Fe0.2PO4/C cathode by investigation of iron sources for lithium-ion batteries

Iron (Fe) substitution is an effective strategy for improving the electrochemical performance of LiMnPO4 which has poor conductivity. Herein, we focus on investigating the effect of substitution of Mn with different iron sources, on the structure and electrochemical performances of the LiMnPO4 materials. The Fe-substituted LiMnPO4/C composites were synthesized via a simple and rational solid-state method, and will be of benefit for engineering applications. The characterization of the materials shows an obvious influence of the iron sources on structure and morphology. The N-LMFP material prepared using soluble FeNO3 as iron sources exhibits an excellent rate capacity of 122 mA h g-1 at 5C, and superior cyclability with a capacity retention of 98.9% after 400 cycles at 2C. The enhanced rate capability and cycling stability of N-LMFP are the result of the lowered electron/ion resistance and the improved reversibility of the reaction, that originates from the homogeneous fine particles and hierarchical structure with large mesopores. This research provides significant guidelines for designing an LiMnPO4 cathode with a high performance.

Stabilization of crystal and interfacial structure of Ni-rich cathode material by vanadium-doping

Stable structure and interface of nickel-rich metal oxides is crucial for practical application of next generation lithium-ion batteries with high energy density. Bulk doping is the promising strategy to improve the structural and interfacial stability of the materials. Herein, we report the impact of vanadium-doping on the structure and electrochemical performance of LiNi_0.88Co_0.09Al_0.03O₂ (NCA88). Vanadium doped in high oxidation state (+5) would lead to alteration of the crystal lattice and Li⁺/Ni²⁺ cation mixing. Those are the main factors determining the cycling and rate capability of the materials. With optimization of vanadium-doping, the preservation of the integrity of the secondary particles of the materials, the enhancement of the diffusion of Li⁺ ions, and alleviation of the side reactions of the electrolyte can be efficiently achieved. As a result, NCA88 doped with vanadium of 1.5 mol % can provide superior cycling stability with capacity retention of 84.3% after 250 cycles at 2C, and rate capability with capacity retention of 65.5% at 10C, as compared to the corresponding values of 58.6% and 55% for the pristine counterpart, respectively. The results might be helpful to the selection of dopants in the design of the nickel-rich materials.

Preparation of the nanorods-assembled and CNTs-embedded LiMnPO4 hollow microspheres for enhanced electrochemical performance of lithium ion batteries

LiMnPO4 is a promising cathode material for lithium-ion batteries, but it has the drawback of poor electronic conductivity and low Li+ diffusivity. Here, we expect to simultaneously improve electron transfer...

Construction of Carbon-Coated LiMn0.5Fe0.5PO4@Li0.33La0.56TiO3 Nanorod Composites for High-Performance Li-Ion Batteries

The carbon-coated LiMn_0.5Fe_0.5PO₄@Li_0.33La_0.56TiO₃ nanorod composites (denoted as C/LMFP@LLTO) have been successfully obtained according to a common hydrothermal synthesis following a post-calcination treatment. The morphology and particle size of LiMn_0.5Fe_0.5PO₄ (denoted as LMFP) are not changed by the coating. All electrode materials exhibit nanorod morphology; they are 100-200 nm in length and 50-100 nm in width. The Li_0.33La_0.56TiO₃ (denoted as LLTO) coating can facilitate the charge transfer to enhance lithiation/delithiation kinetics, leading to an excellent rate performance and cycle stability of an as-obtained C/LMFP@LLTO electrode material. The reversible discharge capacities of C/LMFP@LLTO (3 wt %) at 0.05 and 5 C are 146 and 131.3 mA h g^-1, respectively. After 100 cycles, C/LMFP@LLTO (3 wt %) exhibits an outstanding capacity of 106.4 mA h g^-1 with an 81% capacity retention rate at 5 C, indicating an excellent reversible capacity and good cycle capacity. Therefore, it can be considered that LLTO coating is a prospective pathway to exploit the electrochemical performances of C/LMFP.

Study on xLiVPO4F·yLi3V2(PO4)3/C Composite for High-Performance Cathode Material for Lithium-Ion Batteries

Cathode materials made of xLiVPO₄F·yLi₃V₂(PO₄)₃/C (x:y = 1:0, 2:1, 0:1) are synthesized via a feasible sol-gel method for high-performance lithium-ion batteries. The structures, morphology, and electrochemical properties of the composites are thoroughly investigated. The results show that LiVPO₄F/C, Li₃V₂(PO₄)₃/C, and 2LiVPO₄F·Li₃V₂(PO₄)₃/C can be synthesized under 750°C without the formation of impurities. Meanwhile, the unique morphology of the 2LiVPO₄F·Li₃V₂(PO₄)₃/C composite, which is porous, with nanoflakes adhering to the surface, is revealed. This composite integrates the advantages of LiVPO₄F and Li₃V₂(PO₄)₃. There are four discharge plateaus near 4.2, 4.1, 3.7, and 3.6 V, and the cathode material delivers high capacities of 143.4, 141.6, 133.2, 124.1, and 117.6 mAh g⁻¹ at rates of 0.1, 0.2, 0.5, 1, and 2 C, respectively. More importantly, the discharge capacity can be almost fully recovered when the discharge rate returns to 0.1 C. The study is highly promising for the development of cathode material for LIBs.