Perspective on cycling stability of lithium-iron manganese phosphate for lithium-ion batteries

Lithium-iron manganese phosphates(LiFex Mn_(1-x)PO_(4),0.1<x<0.9)have the merits of high safety and high working voltage.However,they also face the challenges of insufficient conductivity and poor cycling stability.Some progress has been achieved to solve these problems.Herein,we firstly summarized the influence of different electrolyte systems on the electrochemical performance of LiFexMn_(1-x)PO_(4),and then discussed the effect of element doping,lastly studied the influences of conductive layer coating and morphology control on the cycling stability.Finally,the prospects and challenges of developing high-cycling LiFexMn_(1-x)PO_(4) were proposed.

Solvothermal-assisted morphology evolution of nanostructured LiMnPO_4 as high-performance lithium-ion batteries cathode

As a potential substitute for LiFePO4, LiMnPO4 has attracted more and more attention due to its higher energy, showing potential application in electric vehicle（EV） or hybrid electric vehicle（HEV）. In this work,solvothermal method was used to prepare nano-sized LiMnPO4, where ethylene glycol was used as solvent, and lithium acetate（LiAc）, phosphoric acid（H3 PO4） and manganese chloride（MnCl2） were used as precursors. The crystal structure and morphology of the obtained products were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The electrochemical performance was evaluated by charge-discharge cycling, cyclic voltammetry and electrochemical impedance spectroscopy. The results show that the molar ratio of LiAc：H3 PO4：MnCl2 plays a critical role in directing the morphology of LiMnPO4. Large plates transform into irregular nanoparticles when the molar ratio changes from 2：1：1 to 6：1：1. After carbon coating, the product prepared from the 6：1：1 precursor could deliver discharge capacities of 156.9,122.8, and 89.7 mAhg-1 at 0.05 C, 1 C and 10 C, respectively.The capacity retention can be maintained at 85.1% after 200 cycles at 1 C rate for this product.

Microwave-assisted polyol synthesis of LiMnPO4/C and its use as a cathode material in lithium-ion batteries

We synthesized LiMnPO4/C with an ordered olivine structure by using a microwave-assisted polyol process in 2：15 （v/v） water-diethylene glycol mixed solvents at 130℃ for 30min. We also studied how three surfactants-hexadecyltrimethylammonium bromide, polyvinylpyrrolidone k30 （PVPk30）, and polyvinylpyrrolidone k90 （PVPk90）-affected the structure, morphology, and performance of the prepared samples, characterizing them by using X-ray diffraction, scanning electron microscopy, trans- mission electron microscopy, charge/discharge tests, and electrochemical impedance spectroscopy. All the samples prepared with or without surfactant had orthorhombic structures with the Pnmb space group. Surfactant molecules may have acted as crystal-face inhibitors to adjust the oriented growth, morphol- ogy, and particle size of LiMnPO4. The microwave effects could accelerate the reaction and nucleation rates of LiMnPO4 at a lower reaction temperature. The LiMnPO4/C sample prepared with PVPk30 exhib- ited a flaky structure coated with a carbon layer （-2 nm thick）, and it delivered a discharge capacity of 126 mAh/g with a capacity retention ratio of -99.9% after 50 cycles at 1C. Even at 5C, this sample still had a high discharge capacity of 110 mAh/g, demonstrating good rate performance and cycle performance. The improved performance of LiMnPO4 likely came from its nanoflake structure and the thin carbon layer coating its LiMnPO4 particles. Compared with the conventional polyol method, the microwave-assisted polyol method had a much lower reaction time.

High performance 0.9LiMnPO4-0.1LiFePO4/C composite

The rate performance of lithium manganese phosphate is seriously tarnished by its sluggish surface kinetics,which could be addressed by LiFePO4-surface coating.For a higher energy output,here we explore thinner coating layers with 10%and 5%LiFePO4 via the lab-developed DMSO assisted method.The core-shell structured 0.9LiMnPO4-0.1LiFePO4/C maintains a high specific capacity,153,148 and 140 mA hg-1 under 0.1,1 and 5 C respectively,which are the best results for this composition till date.As for 0.95Li MnPO4-0.05 LiFePO4/C,the discharge capacity is lower than 110 mA hg-1 even in 0.1 C,which cannot meet the requirements of practical application.Our approaches push the manganese ratio of LiMnPO4-based composite to 90%from 80%,further improving the energy-density of the olivine phosphates.