富锂锰基正极材料表面改性及电化学性能研究

发布时间：2018-02-28 23:03

本文关键词： 锂离子电池钠离子电池富锂锰基正极材料表面改性电解液添加剂　出处：《上海交通大学》2015年博士论文　论文类型：学位论文

【摘要】：锂离子电池以其高能量密度和长循环寿命等优点,已广泛应用于多种便携器件中。电动汽车和储能电站的开发和应用对未来二次电池提出了更高的要求,可归纳为“三高和两低”:高能量密度、高功率特性、高安全性能、低成本和低(无)污染。以钴酸锂为代表的传统正极材料,其可逆容量一般在200 mAh g-1以下,不能完全满足人们对高性能锂离子电池的迫切需求。因此,研究开发高容量、大倍率的正极材料对进一步提高锂离子的能量密度和功率密度至关重要。近年来,富锂锰基正极材料(简称富锂材料),因其高比容量(250 mAh g-1)和低廉的价格受到广泛关注,被认为具有广泛应用前景的下一代锂离子电池正极材料之一。但是,富锂材料较大的首次不可逆容量损失、较差的循环和倍率性能以及电压衰减等问题阻碍了其应用进程。针对这些关键问题,本论文以Li1.2Ni0.13Mn0.54Co0.13O2(简写为LNMCO)材料为研究对象,从表面包覆、电解液成膜添加剂和复合尖晶石相等方面对富锂材料表面优化调控,提高其电化学性能;结合扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)、电感耦合等离子体发射光谱(ICP)红外光谱(IR)、交流阻抗(EIS)和恒电流间歇滴定(GITT)等方法,详细研究了富锂材料表面组成、结构与电化学性能之间的关系。具体内容如下:1.在富锂材料表面包覆聚酰亚胺(PI)保护层。利用聚酰胺酸(PAA)与金属氧化物间较强的相互作用力在富锂材料表面包覆一层PAA,再经亚胺化热处理将PAA包覆层转变为PI。1.0 wt.%PAA溶液可在富锂材料表面均匀地包覆一层约3纳米的薄膜,而较高浓度PAA溶液(2.5 wt.%和5.0 wt.%)包覆的复合材料颗粒之间有片状高分子膜存在。450℃热亚胺化处理后,PI-LNMCO-450复合材料的红外光谱图中出现三个新峰且XPS结果显示复合材料中Mn的结合能降低,表明亚胺化热处理过程中LNMCO材料与包覆层之间存在电荷转移反应,即材料中+4价Mn吸收PI膜中C=O或苯环的电子,形成Mn(III)···O和Mn(III)···苯环相互作用。电化学测试表明,PI-LNMCO-450材料的循环性能和倍率性能均明显提高,其原因主要包括两方面:(1)PI包覆层将富锂材料和电解液隔离,有效地稳定了电极/电解液界面;(2)材料表面部分+4价锰被还原为+3价锰,有利于锂离子在材料表面迁移。2.采用三(三甲基硅烷)磷酸酯(TMSP)作为电解液添加剂。线性扫描伏安曲线显示,TMSP可先于碳酸酯电解液发生氧化分解反应,有效地提高了电解液在高电压(4.5 V)下的稳定性。XPS和TEM结果表明,在充放电过程中TMSP参与在富锂材料表面形成稳定的SEI膜。在添加1.0 wt.%TMSP电解液中,LNMCO/Li电池表现出稳定的循环性能,50次循环容量保持率达90.8%。3.采用水合肼蒸汽处理富锂材料,调控颗粒表层结构。与高浓度水合肼溶液处理会严重破坏富锂材料的晶体结构相比,水合肼蒸汽处理相对比较温和,并且处理层厚度可控。ICP和XRD结果表明,通过Li+/H+交换反应,水合肼蒸汽可从LNMCO材料Li2MnO3组分中脱出部分锂。TEM照片显示,LNMCO-HV材料内部层状结构得以保持,表面形成一层约3纳米的贫锂层。与LNMCO材料相比,LNMCO-HV材料的首次充电4.5 V平台变短,放电容量和库仑效率均有所提高。300℃热处理可将贫锂层中H+脱出留下锂空位,过渡金属离子迁移并占据锂空位,从而在材料表面形成尖晶石Li1-xM2O4相。LNMCO-HV-300材料的首次放电容量和库仑效率分别高达295.6 mAh g-1和89.5%,其微分电容曲线上~2.8 V的还原峰,对应于锂离子嵌入到尖晶石相八面体16c位。4.探讨了LNMCO材料在钠离子电解液中的离子脱嵌反应。线性扫描伏安曲线显示,1 M NaClO4/PC电解液在4.0 V即开始发生轻微的氧化分解反应,4.75 V以后剧烈分解。在1.7~4.5 V电压范围内,LNMCO/Na电池的循环性能比较差,这与高电压循环时电解液不稳定有关。GITT分析可知,LNMCO/Na电池在首次充电过程中锂离子从富锂材料中脱出,而首次放电过程中则发生锂离子和钠离子共同嵌入。XRD结果表明,NMCO/Na电池首次放电后有富钠相生成,而LNMCO/Na电池,随着循环次数的增加逐渐生成富钠相。添加5.0 vol.%FEC,可以显著地提高1 M NaClO4/PC电解液在高电压下的稳定性。LNMCO/Na电池在该电解液中表现出稳定的循环性能。
[Abstract]:Lithium ion battery with high energy density and long cycle life and other advantages, has been widely used in various portable devices. The development and application of electric vehicles and energy storage power station put forward higher requirements for the next two battery, can be summarized as "three high and two low": high energy density, high power characteristics. High safety performance, low cost and low (no) pollution. The traditional cathode material in lithium cobalt oxide as the representative, the reversible capacity is generally 200 mAh below g-1, can not fully meet the urgent demand for high performance lithium ion batteries. Therefore, the research and development of high capacity, high rate of cathode materials to improve lithium the ion energy density and power density is very important. In recent years, lithium rich manganese based cathode materials (referred to as lithium rich materials), because of its high specific capacity (250 mAh g-1) and low prices attracted widespread attention, is considered to have broad application prospects in the next generation One of the cathode materials for lithium ion batteries. However, lithium rich materials large irreversible capacity loss, the problem of poor circulation and rate performance and the voltage attenuation hinders its application process. Aiming at these questions, this paper takes Li1.2Ni0.13Mn0.54Co0.13O2 (LNMCO) materials as the research object, from the surface coating, film forming electrolyte additive and equal of lithium rich spinel composite material surface optimization, improve its electrochemical performance; scanning electron microscopy (SEM), transmission electron microscopy (TEM), X ray diffraction (XRD), X ray photoelectron spectroscopy (XPS), inductively coupled plasma atomic emission spectrometry (ICP), infrared spectrum (IR) communication the impedance (EIS) and the galvanostatic intermittent titration (GITT) method, a detailed study of the surface of lithium rich materials, the relationship between structure and electrochemical performance. The specific contents are as follows: 1. in lithium rich materials surface Coated polyimide (PI) layer. Using the polyamic acid (PAA) and the strong interaction between metal oxides in lithium rich materials coated with a layer of PAA, and then by imidization heat treatment of PAA thin film coating layer into PI.1.0 wt.%PAA solution can be uniformly coated with a layer of about 3 nm on the surface of lithium rich materials. And the higher concentration of PAA solution (2.5 wt.% and 5 wt.%) between the composite particles coated with a laminar polymer film.450 C imidization treatment, infrared spectra of PI-LNMCO-450 composites in three new peak and XPS results showed that the composite material can reduce the Mn, indicate the existence of the charge transfer reaction between LNMCO materials the imidization process of heat treatment and coating materials, namely +4 Mn C=O valence electronic absorption or benzene ring in PI membrane, the formation of Mn (III) - O and Mn (III) - benzene interaction. The electrochemical tests show that PI-LNMCO-450 The cycle performance and rate capability were improved obviously. The reason mainly includes two aspects: (1) PI coating layer will be lithium rich materials and electrolyte isolation, effectively stabilize the electrode / electrolyte interface; (2) surface +4 of manganese was reduced to +3 Mn, in favor of lithium ion in materials the surface migration of.2. using three (three methyl silane) phosphate (TMSP) as the electrolyte additives. Linear sweep voltammetric curves show that TMSP may precede carbonate electrolyte oxidation decomposition reaction, effectively improve the electrolyte at high voltage (4.5 V) under the stability of.XPS and TEM results showed that in the process of charge and discharge in TMSP the formation of stable SEI film in lithium rich materials surface. With the addition of 1 wt.%TMSP electrolyte, LNMCO/Li battery exhibits stable cycling performance, 50 cycles the capacity retention rate of 90.8%.3. by hydrazine vapor treatment of lithium rich materials, control surface Structure. Compared with the high concentration of hydrazine hydrate solution may cause serious damage to the crystal structure of lithium rich materials, hydrazine hydrate steam treatment was relatively mild and controllable thickness of.ICP and XRD results show that the exchange reaction by Li+/H+, hydrazine hydrate steam from LNMCO materials Li2MnO3 components to remove part lithium.TEM photos showed that LNMCO-HV material the internal layer structure is maintained, poor lithium layer about 3 nm is formed on the surface. Compared with LNMCO, the first charge material LNMCO-HV 4.5 V platform becomes shorter, the discharge capacity and coulombic efficiency were improved at.300 heat treatment can be depleted lithium layers of H+ from left lithium ion migration and transition metal vacancies. Occupy the Li vacancy, resulting in the formation of spinel Li1-xM2O4 phase.LNMCO-HV-300 material on the surface of the first discharge capacity and coulombic efficiency were as high as 295.6 mAh and 89.5% g-1, the differential capacitance curves on ~2.8 V The reduction peak corresponds to the lithium ion embedded into the spinel 16c.4. eight surface of LNMCO material in sodium ion in the electrolyte intercalation reaction. Linear sweep voltammetric curves show that the 1 M NaClO4/PC electrolyte at 4 V appeared mild oxidation decomposition reaction, 4.75 V after severe decomposition in 1.7~4.5. The voltage range of V, the cycle performance of LNMCO/Na battery is relatively poor, and the high voltage cycle when the electrolyte is not stable on the.GITT analysis, LNMCO/Na cells emerge from the lithium rich materials for the first time in charge of lithium ion in the process, and for the first time in the discharge process, lithium ions and sodium ions in common embedded.XRD. The results show that the NMCO/Na battery for the first time discharge after sodium rich phase formation, and LNMCO/Na cells, with the increase of the cycle number gradually generate sodium rich phase. Adding 5 vol.%FEC, 1 M NaClO4/PC can significantly improve the electrolyte under high voltage The stable.LNMCO/Na battery has a stable cycle performance in the electrolyte.

【学位授予单位】：上海交通大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ131.11;TM912

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