Fine Structure and Electrochemical Performance Investigations of Spherical LiMn0.6Fe0.4PO4/C Cathode Material Synthesized via a Spray-Drying Route at Various Calcination Temperatures

LiMnxFe1-xPO4/C is characterized by excellent multiplicative performance and high operating voltage, and as a type of cathode material, it has a high electronic conductivity and thus has received much attention. In this paper, carbon-coated LiMn0.6Fe0.4PO4/C was synthesized using glucose + PEG2000 as the carbon source by wet sanding and spray-drying. The experimental results show that the use of sanding and the spray-drying method can make the particle size distribution of LiMn0.6Fe0.4PO4/C powder more uniform. The initial discharge specific capacity of the LiMn0.6Fe0.4PO4/C battery was 144.3 mA h g-1, and after 100 cycles at 1 C current, the discharge specific capacity of the battery remained at 128.2 mA h g-1 with a cycling efficiency of 94.3%. At the same time, the oxidation states and coordination environments of the elements Fe and Mn were elucidated by X-ray absorption fine structure spectroscopy. And the ex-Fe-MS was tested under different charging and discharging conditions. The sample optimized by the orthogonal test has good cycle stability and multiplication performance.

Strain engineering of Li+ ion migration in olivine phosphate cathode materials LiMPO4 (M = Mn, Fe, Co) and (LiFePO4)n(LiMnPO4)m superlattices

The olivine phosphate family has been widely utilized as cathode materials for high-performance lithium-ion batteries. However, limited energy density and poor rate performance caused by low electronic and ionic conductivities are the main obstacles that need to be overcome for their widespread application. In this work, atomic simulations have been performed to study the effects of lattice strains on the Li⁺ ion migration energy barrier in olivine phosphates LiMPO₄ (M = Mn, Fe, Co) and (LiFePO₄)_n(LiMnPO₄)_m superlattices (SLs). The (LiFePO₄)_n(LiMnPO₄)_m superlattices include three ratios of LFP/LMP, namely SL3 + 1, SL1 + 1 and SL1 + 3, each of which is along three typical (100), (010) and (001) orientations. We mainly discuss two migration paths of Li⁺ ions: the low-energy path A channel parallel to the b-axis and the medium-energy path B channel parallel to the c-axis. It is found that the biaxial tensile strain perpendicular to the migration path is most beneficial to reduce the migration energy barrier of Li⁺ ions, and the strain on the b-axis has a dominant effect on the energy barrier of Li⁺ ion migration. For path A, SL3 + 1 alternating periodically along the (010) orientation can obtain the lowest Li ion migration energy barrier. For path B, SL1 + 3 is the most favorable for Li⁺ ion migration, and there is no significant difference among the three orientations. Our work provides reference values for cathode materials and battery design.

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.

Nano-/Microhierarchical-Structured LiMn0.85Fe0.15PO4 Cathode Material for Advanced Lithium Ion Battery

Nano/microhierarchical-structured LiMn_0.85Fe_0.15PO₄/C cathode materials were prepared by solvothermal synthesis combined with spray pyrolysis. XRD patterns and HRTEM images indicate that the LiMn_0.85Fe_0.15PO₄/C are well crystallized and no impurity is observed. The as-prepared LiMn_0.85Fe_0.15PO₄/C porous spheres (0.5-11 μm) are accumulated by primary nanoparticles (∼50 nm in width, 50-250 nm in length). Adopting sucrose as a carbon source, the cathode delivers a reversible discharge capacity of 171.2 mAh g^-1 at 0.1C, almost exactly its theoretical capacity (∼170 mAh g^-1). Moreover, the composite exhibits high cycle stability without apparent capacity fading after 100 cycles at rates of 0.1C and 1C. The outstanding electrochemical performances are partially due to Fe²⁺ substitution and carbon coating, which improve the electrical conductivity, and importantly, due to its nano-/microhierarchical structure where primary nanoparticles exhibit high electrochemical activity, abundant mesopores benefit electrolyte penetration and the hierarchical structure ensures cycling stability.

Suppression of Lithium Dendrite Formation by Using LAGP-PEO (LiTFSI) Composite Solid Electrolyte and Lithium Metal Anode Modified by PEO (LiTFSI) in All-Solid-State Lithium Batteries

The formation of lithium dendrites is suppressed using a Li_1.5Al_0.5Ge_1.5(PO₄)₃-poly(ethylene oxide) (LAGP-PEO) composite solid electrolyte and a PEO (lithium bis(trifluoromethane)sulfonimide) [PEO (LiTFSI)]-modified lithium metal anode in all-solid-state lithium batteries. The effects on the anode performance based on the PEO content in the composite solid electrolyte and the molecular weight of PEO used to modify the Li anode are studied. The structure, surface morphology, and stability of the composite solid electrolyte are examined by X-ray diffraction spectroscopy, scanning electron microscopy, and electrochemical tests. Results show that the presence of a PEO-500000(LiTFSI) film on a Li anode results in good mechanical properties and satisfactory interface contact features. The film can also prevent Li from reacting with LAGP. Furthermore, the formation of lithium dendrites can be effectively inhibited as the composite solid electrolyte is combined with the PEO film on the Li anode. The ratio of PEO in the composite solid electrolyte can be reduced to a low level of 1 wt %. PEO remains stable even at a high potential of 5.12 V (vs Li/Li⁺). The assembled Li-PEO (LiTFSI)/LAGP-PEO/LiMn_0.8Fe_0.2PO₄ all-solid-state cell can deliver an initial discharge capacity of 160.8 mAh g^-1 and exhibit good cycling stability and rate performance at 50 °C.

Deep Eutectic Solvent Synthesis of LiMnPO₄/C Nanorods as a Cathode Material for Lithium Ion Batteries

Olivine-type LiMnPO₄/C nanorods were successfully synthesized in a chloride/ethylene glycol-based deep eutectic solvent (DES) at 130 °C for 4 h under atmospheric pressure. As-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and electrochemical tests. The prepared LiMnPO₄/C nanorods were coated with a thin carbon layer (approximately 3 nm thick) on the surface and had a length of 100–150 nm and a diameter of 40–55 nm. The prepared rod-like LiMnPO₄/C delivered a discharge capacity of 128 mAh·g⁻¹ with a capacity retention ratio of approximately 93% after 100 cycles at 1 C. Even at 5 C, it still had a discharge capacity of 106 mAh·g⁻¹, thus exhibiting good rate performance and cycle stability. These results demonstrate that the chloride/ethylene glycol-based deep eutectic solvents (DES) can act as a new crystal-face inhibitor to adjust the oriented growth and morphology of LiMnPO₄. Furthermore, deep eutectic solvents provide a new approach in which to control the size and morphology of the particles, which has a wide application in the synthesis of electrode materials with special morphology.

High performance nano-sized LiMn1−xFexPO4 cathode materials for advanced lithium-ion batteries

A series of LiMn_1−xFe_xPO₄ (0 ≤ x ≤ 1) cathode materials with different Mn/Fe ratios have been successfully synthesized by a facile solvothermal method.