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锂硫电池正极材料的制备及性能优化
论文作者:童鞋论文网  论文来源:www.txlunwenw.com  发布时间:2019/10/26 13:26:41  

摘要:锂硫电池因具有较高的理论比容量和能量密度,一直受到科研人员的关注,被认为是继锂离子电池后的下一代储能装置。但是,目前锂硫电池的商业化还存在一系列问题,比如单质硫导电性差、多硫化物的穿梭效应和体积膨胀等;本论文针对这些问题,提出不同的策略来提高锂硫电池的电化学性能,具体研究内容如下:

1.稀酸炭化法制备碳/硫复合材料:我们设计了一种稀酸炭化法制备碳/硫复合材料;常规方法是采用浓酸炭化,经过对比发现,我们提出的稀酸炭化法制备的碳/硫复合材料在粒径和分散性方面都优于浓酸炭化法,将不可控的、急速的炭化过程变得可控、温和,有利于实现大规模的工业化生产。

2.稀酸炭化法在硫正极材料中的优化研究:在稀酸炭化法的基础上,我们设计了一种原位生成单质硫的碳/硫复合材料的制备方法;Na2S2O3·5H2O在酸性条件下可以生成单质硫,再通过稀酸炭化法在单质硫的外围包裹一层焦化碳层,提高单质硫的导电性。通过调整Na2S2O3·5H2O溶液的加入方式和表面活性剂的用量这两个影响复合材料的形貌的因素,制备出了粒径在100-200 nm之间的球形D-C/S复合材料,具有很好的电化学性能,在0.2 C的电流密度下200次循环后的放电比容量为640 mAh g-1,库仑效率保持在95%以上。

3.一步原位碳热还原法制备硫化锂/碳复合材料:我们设计了一种一步原位碳热还原方法制备硫化锂/碳正极材料;通过将硫酸锂和PVP溶解混合后负载在脱脂棉上,经过高温煅烧后制备出硫化锂/碳正极材料。该方法制备出的硫化锂/碳正极材料不需要导电剂和集流体,直接可以作为电极材料使用,避免了硫化锂因化学性质活泼而带来制备极片的困难;在电化学方面也有优异的性能,在电流密度0.2 C下循环100次后,Li2S@C-N-CDC复合材料的放电比容量保持在647.0 mAh g-1左右,库仑效率保持在99%以上。

Lithium-sulfur batteries have been thefocus of researchers because of their high theoretical specific capacity andenergy density, which are also considered to be the next generation of energystorage devices most likely to replace lithium-ion batteries. However, thereare still some problems in the commercialization of lithium-sulfur batteries,such as poor conductivity of elemental sulfur, shuttle effect of polysulfideand volume expansion. In order to solve these problems, this paper proposesdifferent strategies to improve the electrochemical performance oflithium-sulfur batteries. The research contents are as follows:

1.Preparation of carbon/sulfur compositesby dilute acid carbonization: we design a carbon dioxide/sulfur composite bydilute acid carbonization. The conventional method is to use concentrated acidcarbonization. After comparison, the carbon/sulfur composite prepared by thedilute acid carbonization method is superior to the concentrated acidcarbonization method in particle size and dispersibility. This makes theuncontrollable and rapid carbonization process controllable and gentle, whichis beneficial to realize large-scale industrial production.

2. Optimization of dilute acidcarbonization in sulfur cathodes: Based on the dilute acid carbonizationmethod, we design a preparation process of carbon/sulfur composite, whichgenerates elemental sulfur in situ. The elemental sulfur is formed byNa2S2O3·5H2O under acidic conditions and then is coated by a coking carbonlayer by dilute acid carbonization to improve the conductivity. A sphericalD-C/S composite with a particle size between 100-200 nm was prepared byadjusting the morphology of the Na2S2O3·5H2O solution and the amount ofsurfactant. The composite has good electrochemical performance, and thedischarge specific capacity after 200 cycles at a current density of 0.2 C is640 mAh g-1, and the coulombic efficiency is maintained above 95%.

3. Preparation of lithium sulfide/carboncathode by one-step in-situ carbothermal reduction method: we design a one-stepin situ carbothermal reduction method to prepare lithium sulfide/carboncathode. Lithium sulfate and PVP are mixed into a solution and loaded on thedegreasing cotton, and then calcined at a high temperature to prepare a lithiumsulfide/ carbon cathode. The lithium sulfide/carbon cathode material preparedby the method does not need a conductive agent and a current collector and canbe directly used as an electrode material, thereby avoiding the difficulty inpreparing a pole piece due to the active chemical property of lithium sulfide.It also has excellent performance in electrochemistry. After 100 cycles at 0.2 C,the discharge specific capacity of Li2S@C-N-CDC composite is maintained atabout 647.0 mAh g-1, and the coulombic efficiency is maintained above 99%.

关键词:锂硫电池;正极;稀酸炭化法;碳/硫复合材料;硫化锂

lithium-sulfur batteries;cathode;dilute acid carbonization;carbon/sulfur composite;lithium sulfide

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