Lithium ferric manganese phosphate positive electrode material with iron and manganese elements in full-concentration gradient distribution and preparation method of lithium ferric manganese phosphate positive electrode material

Abstract

The invention provides a lithium iron manganese phosphate positive electrode material with iron and manganese elements in full-concentration gradient distribution and a preparation method of the lithium iron manganese phosphate positive electrode material. The lithium iron manganese phosphate positive electrode material comprises a lithium iron manganese phosphate inner core and a thin lithium iron phosphate coating layer coating the surface of the inner core, and in the direction from the center of the lithium manganese iron phosphate core to the surface layer of the core, the content of the manganese element is reduced in a gradient manner, and the content of the iron element is increased in a gradient manner. The preparation method comprises the following steps: (1) adding an iron salt solution and a manganese salt solution into a reactor, adding a phosphorus source compound solution and an ammonia water solution, and carrying out a coprecipitation reaction to form a phosphate precursor core; (2) not adding the manganese salt solution, then carrying out coprecipitation reaction, aging, filtering, washing and drying to obtain precursor particles; (3) uniformly mixing with a lithium source; and (4) carrying out solid-phase reaction. According to the invention, the electrochemical lithium intercalation and deintercalation capability of the material is obviously improved, and the material has excellent electrochemical performance, high tap density and specific discharge capacity and good cycle stability.

Description

technical field [0001] The invention belongs to the technical field of lithium ion batteries, and in particular relates to a lithium iron manganese phosphate cathode material in which iron and manganese elements are distributed in a full concentration gradient and a preparation method thereof. Background technique [0002] With the continuous development of the global economy, the gradual deepening of the energy crisis and the increasing awareness of environmental protection, the power battery industry as a new energy and environmentally friendly low-carbon power battery industry has developed rapidly, and lithium-ion batteries have become many power batteries with their excellent performance and moderate manufacturing costs. mainstream development direction. Lithium-ion batteries currently used mainly include battery systems using lithium cobalt oxide, lithium manganate, ternary cathode materials, and lithium iron phosphate with an olivine structure as cathode materials. ...

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Problems solved by technology

As the proportion of manganese increases, the energy density of the material will increase, and the lithium voltage will be increased from 3.5V to 4.1V, and these two voltages respectively have two charge and discharge platforms (corresponding to Fe 2+ with Fe 3+ , Mn 2+ with Mn 3+ redox reaction between), but at the same time, the polarization of the material in the battery increases, and the discharge capacity and rate performance deteriorate, especially when the manganese content exceeds half, the electrochemical performance of the material deteriorates seriously, which means that simply Increased content will significantly reduce the discharge efficiency of the battery, thereby affecting the battery capacity and safety

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