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The effect of Ni substitution on the performance of LiMnTiO4 material for lithium ion battery

by:dcfpower     2021-03-14
u003cpu003eu003cpu003eThe new generation of chemical power lithium ion secondary batteries, due to their unique advantages such as high energy density and power density, high voltage, low self-discharge rate, no memory effect, light weight, and no pollution, have quickly become The most promising new battery. The cathode material of lithium ion battery will directly affect the performance of lithium battery pack. Currently, commercially available cathode materials include layered LiCoO2, LiNi1/3Co1/3Mn1/3O2, olivine-type LiFePO4 and spinel-type LiMn2O4. Spinel LiMn2O4 has the advantages of cheap raw materials, non-toxicity and high voltage platform. It is an ideal cathode material for lithium-ion batteries. However, its capacity is easily attenuated during charge and discharge cycles. The main reasons are as follows: 1) The disproportionation reaction of Mn3+ on the surface and the erosion of acid in the electrolyte cause the dissolution of Mn, and the generated Mn2+ dissolves into the electrolyte, causing capacity loss; 2) Mn3+ The Jahn-Teller effect caused. The Jahn-Teller effect causes the transformation of the cubic phase to the tetragonal phase in the crystal structure, the lattice parameter c/a value increases, and the structure shrinks and expands greatly, which hinders the channel for lithium ion transmission and destroys the spinel lattice. The contact between particles is loosened, which makes it difficult to de-embed the Li+ u003c/pu003eu003cpu003eu003cpu003eThere are roughly two types of methods to improve the cycle performance of electrode materials: One is to coat the surface of the positive electrode material, which is mainly to coat a layer of oxide or non-oxide particles on the surface of the active material to make The contact area between the electrolyte and the positive active material of the lithium battery pack becomes smaller, which reduces the decomposition of the electrolyte and improves the cycle life of the material at high temperatures; the second is its doping modification, also known as internal structural modification. The doping modification includes cation doping, anion doping and mixed ion doping. For example: Geng et al. [4] used the template method to dope Al into LiMn1.5Ni0.5O4 and found that Al can enhance the stability of the material and improve The capacity of LiMn1.5Ni0.5O4 is between 70 and 120 mAh/g. After Al doping, its capacity is increased to 140 mAh/g, and the capacity retention rate reaches 70% after 200 cycles; Liu et al. [5] B Substituting 10% (atomic ratio) of P in LiMnPO4 can significantly improve the cycle performance and high rate performance of the electrode; an appropriate amount of composite doping with anion and cation Al-F can improve the lithium ion cathode material Li(Ni1/3Co1/3 Mn1/3) The crystallinity of O2 improves the layered structure,u003c/pu003eu003cpu003ethus greatly improving its cycle performance. u003cpu003eFor LiMn2O4 materials, proper doping of appropriate elements can stabilize the material structure, inhibit the dissolution of manganese, and inhibit the Jahn-Teller effect. In recent years, studies have found that [8-9] that Ti4+ replacing Mn4+ in LiMn2O4 can well inhibit the Jahn-Teller effect. The bond energy of TiO bond is 662kJ/mol, which is higher than the 402 kJ/mol of MnO bond, which can form a more stable [Mn2-xTix]O4 structure, thereby suppressing the Jahn-Teller effect. In addition, Ti substitution can reduce part of Mn3+ to Mn2+, reduce the concentration of Mn3+ that causes the Jahn-Teller effect, and increase the discharge capacity while suppressing the Jahn-Teller effect, but there is still a certain gap compared with the theoretical discharge capacity. In the study of spinel LiMn2O4, it was found that Ni replacing Mn (LiMn1.5Ni0.5O4) improved the discharge capacity and cycle stability of electrode materials [10-11]. In order to improve the discharge capacity of LiMnTiO4, this work used sol-gel method combined with solid phase reaction to prepare LiMn1-xNixTiO4 (xu003d0, 0.1, 0.2, 0.3), and studied the influence of Ni substitution on the electrochemical performance of LiMnTiO4. u003c/pu003eu003cpu003eFor more copyright reasons, please check the academic website.u003cpu003eConclusionu003c/pu003eu003cpu003e1) Ni substitution did not change the spinel structure and morphology of LiMnTiO4, nor did it produce or replace it Element-related miscellaneous phases. u003c/pu003eu003cpu003e2) When Ni is used to replace Mn, the amount of replacement should not be too much. If the amount of replacement is too much, the charge and discharge capacity of the electrode material will be significantly attenuated. 3) When the Ni substitution amount is 0.1, the electrochemical performance of LiMnTiO4 has been significantly improved. After 48 cycles, the discharge capacity of LiMn0.9Ni0.1TiO4 is 162.8 mAh/g, and the capacity retention rate is 82.7%. This is mainly due to the reduction of electrode polarization in the redox process after Ni substitution, which facilitates the progress of electrochemical reactions. u003c/pu003eu003c/pu003eu003c/pu003eu003c/pu003eu003c/pu003eu003c/pu003e
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