针对镍锰酸锂正极材料的高电压电解液适配性研究

发布时间：2018-03-27 14:31

本文选题：γ-丁内酯　切入点：戊二腈　出处：《华东理工大学》2017年硕士论文

【摘要】：目前,锂离子电池(LIBs)凭借其高能量密度,高放电平台和长循环寿命已广泛应用于众多领域,锂离子电池在手机、笔记本电脑、数码产品等电子通讯产品中得到广泛应用并占据了主导地位。锂电池现使用电解质多为液体状态的有机电解质,它在较高电压下会持续氧化分解,从而引起正极中过渡金属的溶解,加速电池比容量的衰减。本文从提高电解液在高电压下的稳定性入手,通过电解液溶剂及添加剂的选择,使其在4.35 V和5 V以上的高电压下也正常工作而不发生分解。首先,在商业化的由EC、EMC、DEC和LiPF6组成的基础电解液体系中,分别加入Y-丁内酯(GBL)和戊二腈(GLN)、1%和2%的氟代碳酸乙烯酯(FEC)作为添加剂,改善基础电解液体系在高电压下的性能。研究结果表明,由于Y-丁内酯(GBL)作为电解液添加剂,能在LiNi_(0.5)Mn_(1.5)O_4表面优先氧化分解形成一层稳定的保护膜,有效阻止了电解液的不断氧化分解,能够改善基于LiNi0.5Mn1.504正极的锂离子电池的性能;而戊二腈(GLN)虽然有一个较宽的电化学窗口,能维持电池在低倍率下的循环稳定性,但它与低电位的Li负极间的兼容性随着电流密度的增加而变差,严重影响了LiNi0.5Mn1.504正极材料性能的发挥。另外本文还研究了 1%和2%氟代碳酸乙烯酯(FEC)对LiNi_(0.5)Mn_(1.5)O_4(LNMO)电化学性能的影响,实验结果表明:FEC显著提高了 LiNi0.5Mn1.504的循环性能和比容量。150圈后,1%FEC作为电解液的半电池比容量为106.7 mA h g~(-1),容量保持率为91.1%。2%FEC作为电解液的半电池比容量为113.5 mAh g~(-1),容量保持率为96.2%。并且,2%FEC体系能够在2 C倍率下维持105.7 mAh g~(-1)的比容量。而只含有基础电解液的LiNi_(0.5)Mn_(1.5)O_4/Li半电池,1 C循环150圈后比容量仅为91.3 mAh g~(-1),容量保持率为82.3%。测试研究表明:FEC的优先氧化有利于形成高导电性能的膜,该膜由少量低电导率的物质组成。另外,2%FEC比1%FEC更有利于形成一层均一且致密的膜。
[Abstract]:Li-ion battery has been widely used in many fields because of its high energy density, high discharge platform and long cycle life. Electronic communications products, such as digital products, are widely used and dominate. Lithium batteries now use organic electrolytes in liquid state, which continue to be oxidized and decomposed at higher voltages. Therefore, the solution of transition metal in the positive electrode and the attenuation of the specific capacity of the battery are accelerated. In this paper, the stability of the electrolyte under high voltage is improved, and the selection of solvent and additive is carried out. It works normally at a high voltage of 4.35 V and over 5 V without decomposing. First, in a commercial basic electrolyte system composed of EMC DEC and LiPF6, Y-Butyrolactone (GBL) and pentanilonitrile (GLN) (1% and 2%) were added as additives to improve the performance of the basic electrolyte system at high voltage. The results showed that because Y-Butyrolactone (GBL) was used as electrolyte additive, It can preferentially oxidize and decompose on the surface of LiNi_(0.5)Mn_(1.5)O_4 to form a stable protective film, which effectively prevents the continuous oxidation decomposition of electrolyte and improves the performance of lithium-ion battery based on LiNi0.5Mn1.504 positive electrode, while glutaric nitrile GLN) has a wide electrochemical window. It can maintain the cycle stability of the battery at low rate, but its compatibility with the Li negative electrode with low potential becomes worse with the increase of current density. In addition, the effects of 1% and 2% ethylfluorocarbonate on the electrochemical properties of LiNiNiLi-0.5MnM / Mn-Mn-MOS have been studied, and the effects of 1% and 2% ethylfluorocarbonate on the electrochemical properties of LNMOs have also been studied. The experimental results show that the cycle performance and specific capacity of LiNi0.5Mn1.504 were significantly improved by 1: FEC. The specific capacity of 1 C as electrolyte was 106.7 Ma / h / g ~ (-1) / L ~ (-1), and the capacity retention ratio was 91. 1 路2 ~ (2) C as electrolyte. The specific capacity of half cell was 113.5 mAh / L ~ (-1). The specific capacity of LiNi_(0.5)Mn_(1.5)O_4/Li semilayer containing only basic electrolyte was 91.3 mAh / g ~ (-1), and the specific capacity was 91.3 mAh / g ~ (-1) after 150 cycles. The specific capacity of 2C system could maintain 105.7 mAh / g ~ (-1) at the rate of 2 C. The measurement showed that the specific capacity of LiNi_(0.5)Mn_(1.5)O_4/Li half-cell containing basic electrolyte was only 91.3 mAh / g ~ (-1) / L ~ (-1), and the capacity retention was 82.3%. The experimental results show that the preferential oxidation of the FEC is beneficial to the formation of films with high conductivity. The film is composed of a small amount of materials with low conductivity. In addition, 2C is more favorable than 1C to form a uniform and compact film.
【学位授予单位】：华东理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O646;TM912

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