The Design Of Lithium Vanadate/Carbon Composite And Its Lithium Storage Properties

Reducing carbon emissions,coping with global climate change and transitioning from fossil energy to renewable and clean energy are urgent issues in today’s society.The development of energy storage devices plays a crucial role in the utilization of clean energy sources such as solar and wind power,as well as the popularization of zero-emission electric vehicles.Lithium-ion batteries（LIBs）dominate the energy storage market due to their combination of high energy and power density,long cycle stability,and environmental friendliness.The electrochemical performance of LIBs depends seriously on electrode materials,thus searching new electrode materials with better performance is particularly important for the development of high-performance LIBs.Compared with cathode materials which were widely studied,there are limited types of commercial anode materials.As a new insertion type anode material,Li₃VO₄（LVO）has the advantages of high specific capacity and good safety,demonstrating great potential for practical application.However,the intrinsic low electrical conductivity and the difficulty in morphology regulation of LVO result in unsatisfactory electrochemical performance.In this paper,polymer material is used as carbon source to combine with LVO and to regulate the morphology,and the electrochemical performance of the as-prepared LVO/C composites are further studied.The main research contents and conclusions are as follows:1.Carbon nanosheets were prepared by a two-step self-induction strategy of sintering and water washing,using low cost industrial water-absorbent resin as source（WAR-CNFs）.The WAR-CNFs exhibit graphitized edges and interconnected crystallites and amorphous carbons in the interior,which are beneficial for efficient lithium ions diffusion and electron transfer.These feature results in excellent electrochemical performance,suggesting the WAR-CNFs could be used as ideal active material and carbon source for constructing advanced composite anode materials for LIBs.Li₃VO₄/C composites（LVO/C）were obtained by mixing an appropriate amount of WAR-CNFs with LVO precursor,treated by hydrothermal reaction and sintering.The LVO/C exhibits good electrochemical performance as anode for LIB.A reversible capacity of 407.3 mAh g^-1 can be maintained after 200 cycles at 0.2 A g^-1.After periodic rate performance testing from 0.2 A g^-1 to 4.0 A g^-1 over 310 cycles,the capacity of the LVO/C could be fully reverted.Even under a high discharging/charging current density of4.0/2.0 A g^-1,the LVO/C exhibits stable cycling over 5000 times.2.Bifunctional lithium polyacrylate（PAALi）was prepared according to the preparation of water-absorbent resin.N-doped C coated LVO composites（LC-NC@LVO）were designed and prepared via spray drying technology and solid phase sintering,using PAALi as both carbon and Li sources.The as-prepared LC-NC@LVO exhibits excellent electrochemical performance as anode for LIBs.It shows high capacity of 596.2 mAh g^-1 at 0.5 A g^-1and excellent rate performance(i.e.,full capacity recovert after 10 periods from 0.1 to 6.0 A g^-1over 600 cycles).When cycling at high discharging/charging current of 10.0/5.0 A g^-1 for 5000cycles,an average capacity attenuation is as low as 0.003%.In addition,Li₃V₂（PO₄）₃/C（LVP）was prepared by similar method,and the LVP//LC-NC@LVO full battery displays good rate performance,showing discharge capacity of 271.4 mAh g^-1 after 600 cycles at 1.0 A g^-1.3.LVO/N-doped C nanosheets（LVO@NC NSs）were synthesized by spray drying,using polyvinyl alcohol（C₂H₄O）_n（PVA）as carbon source and morphology template.The two-dimensional（2D）morphology and cross-linked LVO@NC particles lead to high reactivity and excellent rate performance.When cycling at 0.2 A g^-1,the LVO@NC NSs display a charging capacity of 628.4 mAh g^-1 after 300 cycles,which is close to the initial charging capacity.A high charging capacity of 610.3 mAh g^-1 is maintained after 9 periods of rate performance test from 0.1 to 6.0 A g^-1 for 460 cycles.The LVO@NC NSs also show excellent long cycle performance at discharging/charging current density of 6.0/3.0 A g^-1,providing a high charge capacity of 277.0 mAh g^-1 after 5000 cycles.At the same time,A LFP//LVO@NC NSs full cell was assembled with modified commercial Li Fe PO₄（LFP）.Under a current density of 1.0 A g^-1,the full cell displays a capacity of 165.5 mAh g^-1 after 1000 cycles,showing good cyclability.The energy density of the full cell is 169.0 Wh kg^-1,which is higher than that of some LVO or LFP based full cells reported in literatures.