锂离子电池容量衰减机理和界面反应研究

Capacity Fade Mechanisms and Side

Reactions in

Lithium-Ion Batteries

Pankaj Arorat and Ralph E. White Center For Electrochemical Engineering, Department of Chemical Engineering, University of South Carolina,Columbia, South Carolina 29208, USA

ABSTRACT

The capacity of a lithium-ion battery decreases during cycling. This capacity loss or fade occurs due to several different mechanisms which are due to or are associated with unwanted side reactions that occur in these batteries. These reactions occur during overcharge or overdischarge and cause electrolyte decomposition, passive film formation, active material dissolution, and other phenomena. These capacity loss mechanisms are not included in the present lithium-ion battery mathematical models available in the open literature. Consequently, these models cannot be used to predict cell performance during cycling and under abuse conditions. This article presents a review of the current literature on capacity fade mechanisms and attempts to describe the information needed and the directions that may be taken to include these mechanisms in advanced lithium-ion battery models。锂离子电池容量衰减机

理和界面反应研究

作者：Pankaj Arorat and Ralph E. White

美国，南卡罗来纳29208，哥伦比亚，南卡罗来纳州大学，化工学院化工系

摘要

锂电池在循环过程中，其容量会逐渐衰减。而出现容量衰减主要归因于几个不同的机理，这些机理大多与电池内部的界面反应相关，这些反应持续性的发生在电池的充放电环节，并且引起电解液的分解、钝化膜的形成、活性材料的溶解等其它现象。关于容量衰减的机理在目前公开的锂离子电池数学模型的文献中并未加以阐述，因此在锂电池循环过程中和处于苛刻的条件下，我们无法通过模型来对锂电池的性能作出有效的预测。本篇文章将陈述容量衰减的机理，并且试着去解释其本质，为构建先进的锂电池模型指明方向。

lntroduction

The typical lithium-ion cell(Fig. 1) is made up of a coke or graphite negative electrode, an electrolyte which serves as an ionic path between electrodes and separates the two materials, and a metal oxide (such as LiCoO2, LiMn2O4, or LiNiO2) positive electrode. This secondary (rechargeable) lithium-ion cell has been commercialized only

概论

传统的锂电池由碳或石墨负极材料、作为电极间的离子传输通道的电解液、金属氧化物（例如LiCoO2、LiMn2O4、LiNiO2）正极材料三部分组成，这种二次（可充电）电池已经商业化。依照这种原理制作的锂电池已

recently.47 Batteries based on this concept have reached the consumer market, and lithium-ion electric vehicle batteries are under study in industry. The lithium-ion battery market has been in a period of tremendous growth ever since Sony introduced the first commercial cell in 1990.With energy density exceeding 130 Wh/kg (e.g., Matsushita CGR 17500)and cycle life of more than 1000 cycles (e.g., Sony 18650)in many cases, the lithium-ion battery system has become increasingly popular in applications ，such as cellular phones, portable computers, and camcorders. As more lithium-ion battery manufacturers enter the market and new materials are developed, cost reduction should spur growth in new applications. Several manufacturers such as Sony Corporation, Sanyo Electric Company, Matsushita Electric Industrial Company, Moli Energy Limited, and A&T Battery Corporation have started manufacturing lithium-ion batteries for cellular phones and laptop computers. Yoda has considered this advancement and described a future battery society in which the lithium-ion battery plays a dominant role.经形成稳定的消费者市场，同时锂离子动力电池也在进行工业化研究。自从1990年，Sony制造出第一批商业化电池开始，锂电池市场开始进入繁荣时期。由于具有超过130wh/kg（matsushita CGR 17500）的能量密度和超过1000次循环的优势，锂电池在移动电话、手提电脑、便携式摄像机等设备领域得到更加广泛的应用。随着更多的锂电池生产商进入市场，新型材料也被陆续开发出来，同时成本控制也成为新产品增长的关键因素。像索尼电器、三洋电器公司、松下电器、莫里能源有限公司（加拿大）、日本A&T 电器公司都已经在移动电话和便携式电脑等产业开始锂电池应用商业化。Yoda也已经认识到锂电池的发展趋势，并且在将来的电池能源时代，锂离子电池将扮演者关键的角色。

Several mathematical models of these lithium-ion cells have been published.Unfortunately, none of these models include capacity fade processes explicitly in their mathematical description of battery behavior. The objective of the present work is to review the current understanding of the mechanisms of capacity fade in lithiumion batteries. Advances in modeling lithium-ion cells must result from improvements in the fundamental understanding of these processes and the collection of relevant experimental data.

关于锂离子电池的数学模型，已经有相关文献进行阐述，然而遗憾的是至今没有一篇文献能就容量衰减机理进行明确解释，而本文将会在锂电池容量衰减机理进行详细阐述。先进的锂电池模型必须建立在加深对这些过程的基本理解和实验数据的整理归纳的基础之上。

Some of the processes that are known to lead to capacity fade in lithium-ion cells are lithium deposition (overcharge conditions), electrolyte decomposition, active material dissolution, phase changes in the insertion electrode materials, and passive film formation over the electrode and current collector surfaces. Quantifying these degradation processes will improve the predictive capability of battery models ultimately leading to less expensive and higher quality batteries. Significant improvements are required in performance standards such as energy density and cycle life, while maintaining high environmental,safety, and cost standards. Such progress will require considerable advances in our understanding of electrode and electrolyte materials, and the fundamental physical and chemical processes that lead to capacity loss and resistance increase in commercial lithium-ion batteries. The process of developing mathematical models for lithiumion cells that contain these capacity fade processes not only provides a tool for battery design but also provides a means of understanding better how those processes occur.

一些常见的引起锂电池容量衰减的因素包括1、锂枝晶的生成（过充电压条件下）2、电解液分解3、活性材料的溶解4、电极材料嵌锂过程中发生相变5、电极材料和集流体表面钝化膜的形成。对以上这些降解过程进行量化，将能够提升电池模型的电池容量，并最终制造出成本低、质量好的电池，能量密度和循环寿命是作为提升电池性能的重要指标，同时电池的安全性能、环境友好程度、成本标准也是衡量电池的指标。在此过程中，我们需要对电解液和电极材料有更深层次的理解，并且对商业化锂电池体系中引起容量衰减、阻抗增加的基本物理原理和化学过程做出进一步探究。构建包含这些容量衰减因素的锂电池数字模型不仅能为锂电池的设计提供帮助，更为探究这些因素如何发生提供方法。

Present Lithium-Ion Battery Models

The development of a detailed mathematical model is important to the design and optimization of lithium secondary cells and critical in their scale-up. West et al. developed a pseudo two-dimensional model of a single porous insertion electrode accounting for transport in the solution phase for a binary electrolyte with constant physical properties and diffusion of lithium ions into the cylindrical electrode particles. The insertion process was assumed to be diffusion limited, and hence charge-transfer resistance at the interface between electrolyte and active material was neglected. Later Mao and White developed a similar model with the addition of a separator adjacent to the porous insertion electrode.These models cover only a single porous electrode; thus, they do not have the advantages of a full-cell-sandwich model for the treatment of complex, interacting phenomena between the cell layers. These models confine themselves to treating insertion into TiS

2

. with the kinetics for the insertion process assumed to be infinitely fast. Spotnitz et al.accounted for electrode kinetics in their

model for discharge of the TiS

2

intercalation cathode.

The galvanostatic charge and discharge of a lithium metal/solid polymer separator insertion positive electrode cell was modeled using concentrated-solution theory by Doyle et al.The model is general enough to include a wide range of separator materials, lithium salts, and composite insertion electrodes. Concentrated-solution theory is used to

如今的锂离子电池模型一种详细的数字模型的构建对于锂离子二次电池的结构设计和性能优化显得极其重要，并且在后续的电池比例扩大过程中起到决定性的作用。西方学者首先构建出一种虚拟的二维模型，在该模型中，存在着单一的多孔可嵌入的电极，它能够保证具有常数物理性质的二元电解液在液态环境中传输，并且能让锂离子在电极的球形颗粒中扩散，锂离子的嵌入过程被认为是扩散能力有限的，因此在电解液和电极材料界面形成的电荷转移电阻通常是被忽略不计的。随后Later Mao和White构建出另外一种相似的模型，此模型中，在多孔的嵌入电极相邻处加入隔膜。这些模型中都只包含一个多孔电极，因此它们不像“三明治”模型那样具备层间相互作用合成处理的优势。在这些模型中，它们将自己定位为TiS2的嵌入处理，并且认为该嵌入过程中的动力学是无限快的，其中Spotnitz学者对TiS2嵌入式正极在放电过程中的电极动力学进行过相关研究。

Doyle学者通过溶液浓度理论构建出由锂金属/固态聚合物隔膜/可嵌入的活性材料三部分组成的恒流充放电体系。该模型一般包括广泛的隔膜材料、锂盐和复合式插入电极。溶液浓度理论则可以解释粒子传输

describe the transport processes, as it has been concluded that ion pairing and ion association are very important in solid polymer electrolytes.This approach also provides advantages over dilute solution theory to account for volume changes. Butler-Volmertype kinetic expressions were used in this model to account for the kinetics of the charge-transfer processes at each electrode. The positive electrode insertion process was described using Pick's law with a constant lithium diffusion coefficient in the active material. The volume changes in the system and film formation at the lithium/polymer interface were neglected and a very simplistic case of constant electrode film resistances was considered. Long-term degradation of the cell due to irreversible reactions (side reactions) or loss of interfacial contact is not predictable using this model.

Fuller et al developed a general model for lithiumion insertion cells that can be applied to any pair of lithium-ion insertion electrodes and any binary electrolyte system given the requisite physical property data. Fuller et al's work demonstrated the importance of knowing the dependence of the open-circuit potential on the state of charge for the insertion materials used in lithium-ion cells. The slopes of these curves control the current distribution inside the porous electrodes, with more sloped open-circuit potential functions leading to more uniform current distributions and hence better utilization of active material. Optimization studies were carried out for the Beilcore plastic lithium-ion system.The model was also used to predict the effects of relaxation time on multiple charge-discharge cycles and on peak power.

Doyle et al.modified the dual lithium-ion 过程，并且认为在固态聚合物电解质环境中，离子的配对和结合是相当重要的，相对于稀溶液理论，这种模型在体积变化上具备优势。？这个模型要运用Butler-Volmertype运动学公式去计算每个电极中电荷转移过程中的动力学。在正极材料的嵌入过程中，利用菲克定理来计算活性材料中锂离子扩散系数，整个体系中体积变化和锂与聚合物界面形成的钝化膜均忽略不计，但是会将电极界面电阻作为恒量纳入考虑范围。通过这种模型，我们无法预测由不可逆反应（副反应）或界面接触损失引起的持续性衰减。

富勒等人构建出锂离子嵌入式电池的综合性模型，这种模型能兼容各种类型的锂离子嵌入式电极和二元电解液形成的体系，这能测定出我们想要的物理属性数据。富勒等人的工作阐述了理解充电状态的开路电压对于锂离子电池嵌入材料应用的重要性。通过这些曲线的斜率可以控制多孔电极内部的电流分布，利用开路电压曲线函数来更好的统一电流分布，因此使活性材料得到更好的使用，而关于贝尔塑料锂离子电池系统的最优化设计已经完成，这个模型可以预测由弛豫时间给电池多次充放电循环和峰值功率带来的影响。

Doyle学者修改了双电

model to include film resistances on both electrodes and made direct comparisons with

experimental cell data for the Li

x C

6

/LiPF

6

,

ethylene carbonate/dimethyl carbonate

(EC/DMC), Kynar FLEX/Li

y Mn

2

O

4

system.

Comparisons between data and the numerical simulations suggested that there is additional resistance present in the system not predicted by present models. The discharge performance of the cells was described satisfactorily by including either a film resistance on the electrode particles or by contact resistances between the cell layers or current-collector interfaces. One emphasis of this work was in the use of the battery model for the design and optimization of the cell for particular applications using simulated Ragone plots.

Thermal modeling is very important for lithium batteries because heat produced during discharge may cause either irreversible side reactions or melting of metallic lithium, Chen and Evans carried out a thermal analysts of lithiumion batteries during charge-discharge and thermal runaway using an energy balance and a simplified description of the electrochemical behavior of the system.Their analysis of heat transport and the existence of highly localized heat sources due to battery abuse indicated that localized heating may raise the battery temperature very quickly to the thermal runaway onset temperature, above which it may keep increasing rapidly due to exothermic side reactions triggered at high temperature. Pals and Newman developed a model to predict the thermal behavior of lithium metal-solid polymer electrolyte cells and cell stacks. This model coupled an integrated energy balance to a fullcell-sandwich model of the electrochemical behavior of the cells. Both of these models emphasized the importance of considerations of heat removal and thermal 极锂离子电池模型，他考虑到两电极表面的钝化膜阻抗，并且制备出LiC6/LiPF6 EC/DMC(阿柯玛股份有限公司)/Li y Mn2O4电池体系测试出的相关比对数据，对比实验数据和数字模型可以得出在该系统中出现的附加阻抗，而这个阻抗无法通过现有的模型进行预测。在将活性材料表面的钝化膜阻抗和电极间的接触阻抗或集电器的界面阻抗纳入考虑范围后，该电池的放电性能令人满意。此项工作的重点是利用模拟Ragone 图来进行电池设计和最优化应用。

热反应建模也是锂电池的重要组成部分，通常认为在放电过程中产生的热量将会导致不可逆的副反应和金属锂的溶解。Chen 和Evans两人制备出一套关于锂电池热分解系统，当电池处于充放电状态或热失控状态，通过能量平衡和简单描述该系统的电化学行为来构建模型，他们关于由电池滥用引起的热量传输分析和局部温度过高的理论表明：局部升温可能会很快地引起电池温度升高以致电池热失控，超出设定温度后，高温将会引发放热性界面反应从而使整个电池的温度急剧上升。Pals和Newman也构建出一种模型，利用该模型可以预测金属固态聚合物电解质电池和电池推的热反应，这个模型将综合能量平衡系统与“三明治”式的全电池模型

control in lithium-polymer battery systems. 相联接，从而测定整个电池

的电化学行为，以上所有模

型均强调锂离子聚合物电

池系统的热散失和热控制

的重要性。

Verbrugge and Koch developed a mathematical model for lithium intercalation processes associated with a cylindrical carbon microfiber. They characterized and modeled the lithium intercalation process in single-fiber carbon microelectrodes including transport processes in both phases and the kinetics of charge transfer at the interface. The primary purpose of the model was to predict the potential as a function of fractional occupancy of intercalated lithium. The overcharge protection for a Li/TiS

2

, cell using redox additives has been theoretically analyzed in terms of a finite linear diffusion model by Narayanan et al。

Darling and Newman modeled a porous intercalation cathode with two characteristic particle sizes.They reported that electrodes with a particle size distribution show modestly inferior capacity-rate behavior and relaxation on open circuit is substantially faster when the particles are uniformly sized. Nagarajan et al modeled the effect of particle size distribution on the intercalation electrode behavior during discharge based on packing theory.They observed that during pulse discharge, an electrode consisting of a binary mixture displays higher discharge capacity than an electrode consisting of singlesized particles. The current from the smaller particles reverses direction during the rest period which cannot be observed in the case of an electrode comprised of the same-sized particles. Recently Darling and Newman made a first attempt to model side reactions in lithium batteries by incorporating a solvent oxidation side reaction into a lithium-ion battery model, Even though a simplified treatment of the oxidation reaction was used, their model was able to make several interesting conclusions about self-discharge processes in these cells and their impact on positive electrode state-of-charge.

Verbrugge和Koch构建成一个关于锂离子嵌入圆柱形碳纤维的数字化模型，该模型可以表征并且可以模拟锂离子在单个碳纤维电极中的嵌入过程。包括锂离子在两相中的传输和界面传输动力学，该模型主要意图是为了预测嵌入的锂离子数量和电动势函数关系。在Nareyamal等学者构建的有限线性扩散模型中，理论分析了可以通过氧化还原添加剂来对Li/TiS2电池进行过充保护的结论。

Darling和Newman构建成两种不同粒径尺寸的多孔嵌入式正极模型，他们表明当材料的颗粒尺寸分布不不均匀时，将会导致较低的容量保持率和较快的自放电现象。？Nagarajan 等学者研究了在充放电过程中颗粒尺寸分布对嵌入式电极的影响？，他们发现在放电过程中，二种粒度混合电极要比单一尺寸颗粒电极具有更高的放电容量。在后期放电过程中，小颗粒里面形成的电流将会改变方向，而这种现象在粒径分布均匀的电极里面不会存在。最近Darling和Newman 开始尝试构建锂电池副反应模型，他们的想法是在锂电池模型中引入溶液氧化副反应系统，尽管对氧化反应进行了简单处理，但他们的模型仍然在电池自放电过程以及它对正极电极充电状态的影响方面能得出一些有价值的结论。

A number of models having varying degrees of sophistication have been developed for lithium rechargeable batteries. For the most part, these models consider the ideal behavior of the systems, neglecting the phenomena that lead to losses in capacity and rate capability during repeated charge-discharge cycles. Fundamental models of these latter phenomena are less common because these processes are not as well understood. Also, models of failure modes in batteries do net usually have general applicability to a wide range of systems. However, the importance of these phenomena in the safe and efficient operation of high-energy lithium-ion batteries requires that they be incorporated into future battery models.

Capacity Fading Phenomenon

Side reactions and degradation processes in lithium-ion batteries may cause a number of undesirable effects leading to capacity loss. Johnson and White have shown that the capacities of commercial lithium-ion cells fade by ca. 10-40% during the first 450 cycles.A flow chart describing many of the processes leading to capacity fade is shown in Fig. 2. In Fig. 3, the capacity fade processes are shown on half-cell discharge curves. This gives a clearer picture of the processes by demonstrating where each is expected to manifest itself during operation of the battery Below, we discuss each of these processes in some detail, after first discussing the general topic of capacity balance.

Capacity Balancing in Lithium-Ion Cells

Lithium-ion cells operate by cycling lithium ions between two insertion electrode hosts having different insertion energies. For optimum performance, the ratio of the lithium-ion capacities of the two host materials should be balanced. Capacity balancing refers to the optimization of the

关于锂离子二次电池已经构建出不同程度复杂性的模型，然而它们大部分都只是电池的理想状态，而忽略了在充放电循环过程中引起容量衰减和容量保持率下降的内部因素。关于后面这些现象的模型原理也不尽相同，因为这些过程还没有被完全解释清楚，同样那些失败的电池模型则没有在广泛的体系中得到应用，然而对于高能量锂电池的安全性和效率性能的重要性来讲，它们仍然有可能纳入到未来的电池模型中。

容量衰减现象

锂电池中的界面反应和衰减过程将会引起一系列负面影响导致容量衰减。Johnson和White展示了商业锂电池在450此循环后容量衰减10%~40%，如图2为一些导致容量衰减过程的流程图，如图3为半电池容量衰减过程的放电曲线。通过放电曲线可以清楚的向我们演示过程。在电池工作期间，我们可以预测该电池每一点的状态。以下我们将详细讨论每一个过程，随后将讨论容量平衡主题。

锂电池容量平衡

在锂电池循环过程中，两个嵌入电极有着不同的嵌入能量，为了达到最佳的性能，两电极的材料重量需要相互匹配。容量平衡是指通过对两电极材料质量进行最优化匹配，使得材料处

mass loading in the two electrodes to achieve the maximum capacity (or energy) from the battery under conditions of steady cycling. Due to the practical importance of this subject for maximizing cell performance, as well as the safety implications with poorly balanced cells, this subject has been discussed in the literature by several authors。

The condition for balanced capacities in a lithium-ion cell can be written in terms of a ratio γ of active masses in the electrodes. Written as a ratio of positive to negative

electrode masses, this expression is

This equation says that the desired mass ratio depends on the relative coulombic capacities of the two electrodes (C is in units of mAh/g) and the amount of cyclable lithium in each. The cyclable lithium is quantified in terms of the range of lithium stoichiometry in the insertion electrode that can be cycled reversibly with the notation that Δx refers to the range of negative electrode stoichiometry and Δy to the positive electrode. For some insertion materials, which have several plateaus over which lithium can be inserted and deinserted, one may choose to cycle over only a limited range of stoichiometry for reversibility or safety reasons. In these cases, the stoichiometric range entered in the above formula would be reduced from its maximum value. 于稳定循环状态时，电池能释放出最大容量。由于最大限度地提高电池的性能和较差平衡电池的安全性能两个主题具有实际意义，有关作者已经在文献中进行过讨论。

锂电池容量平衡的条件为活性物质质量比γ，它表示正极活性材料质量与负极活性材料质量之比，公式如下：

这个公示表明所需的质量比取决于两电极相对库伦容量（C的单位为mAh/g）和每个循环过程中的脱嵌锂量。可循环锂量是指在嵌入电极能进行可逆脱嵌的锂离子，可以用Δx 表示负极化学计量学的范围，Δy表示正极化学计量学范围，相对于一些嵌入材料，它在锂离子进行嵌入和脱出过程中会形成一段电压平台，考虑到电池的可逆性和安全性能，我们可以选择在一个有限的锂量范围内进行循环，在这些情况下，上述公式中输入的化学计量范围将从它的最大值开始降低。

For example, consider the case of a lithium-ion cell having a petroleum coke negative electrode and a lithium manganese oxide spinel positive electrode. By choice, we can assign useful ranges of stoichiometries for the two electrode materials of 0.61 for the coke and 0.83 for the lithium manganese oxide. These stoichiometric ranges correspond to the following electrochemical processes ：

例如，以石油焦炭负极材料和尖晶石型锰酸锂正极材料组装成的锂电池，我们分别为两个电极材料设定锂离子化学计量，其中负极为0.61，正极为0.83。以上化学计量符合以下电化学过程：

The active mass ratio needed to cycle these two materials in the manner shown here is equal to 1.85. This is calculated by using the theoretical capacities of both positive and

negative electrode (C

+ = 148 mAh/g and C

－

=372

mAh/g), equal to F divided by the molecular weight of the electrode material in its discharged state。

The situation above describes an “ideal”lithium-ion cell in which the capacity balance does not change over the life of the cell. For an ideal cell, the initial lithium capacity available for cycling is constant over the life of the battery .Unfortunately the true case in actual lithium-ion batteries is more complicated than this, and side reactions and secondary processes are able to perturb the capacity balance from its ideal state. The actual optimized active mass ratio is ca.

2.05-2.15 for the coke/LiMn

2O

4

system, which

corresponds to 14% excess capacity in the positive electrode. This excess capacity is a measure of the amount of lithium needed to form a stable film over the electrode surfaces. A major process that affects the capacity balance is the initial formation period needed to passivate carbon-based electrodes. It is now well known that carbonaceous lithium insertion electrodes have irreversible capacity associated with the initial charging cycles.This irreversible capacity loss is thought to result in the formation of a lithium 如上两种材料的循环方式，此时的活性物质比为1.85。可以通过正负极的理论容量（C

＋

=148mAh/g，C －

=372mAh/g）等同于F？除以放电状态的电极材料分子量。

所谓理想的锂离子电池条件为在电池的使用过程中，其平衡容量不会发生改变。例如在理想的锂电池体系中，在电池的整个循环过程中有效初始容量作为可逆循环容量，恒定不变。遗憾的是，现实中锂离子电池则复杂许多。界面反应和继发过程将会破坏其平衡容量的理想状态，在焦炭/LiMn2O4电池体系中，实际最优活性质量比大约为2.05~2.15，对应于正极材料中14%的剩余容量。这种多余的锂量主要用于在电极表面形成稳定的界面膜，碳基电极的钝化层初步形成时期将会是影响容量平衡的重要过程。众所周知，含碳的锂插入电极的不可逆容量与其最初充电周期息息相关，我们认为损失的不可逆容量是由

conducting solid electrolyte interface (SEI) layer on the surface of the carbon, while in the process consuming some portion of the cyclable lithium ions in the cell. The loss of cyclable lithium to create this passivation layer has a profound impact on the capacity balance in the cell because it can remove a significant portion of the cyclable lithium depending on the type of carbon used.

If the cyclable lithium in the cell is reduced due to side reactions of any type, the capacity balance is changed irreversibly and the degree of lithium insertion in both electrodes during cell cycling is changed. Consider the case of the initial carbon passivation process that occurs on all lithium-ion cells using carbon-based electrodes. The cell is assembled initially in the discharged state, with the carbon free of lithium and the metal oxide positive electrode at its maximum lithium content. The amount of lithium in either electrode can be represented as shown in Fig. 4, which illustrates the difference between the ideal and actual

carbon/LiMn

2O

4

lithium-ion system during the

first few cycles.

In an ideal lithium-ion cell (Fig. 4a), all of the lithium should be intercalated into the negative electrode from the positive electrode during the first charge. Similarly all of the lithium ions should be intercalated back into the positive electrode during the first discharge. In an actual lithium-ion cell, upon charging the cell for the first time, some

portion of the lithium removed from the LiMn

2O 4

positive electrode goes into the irreversible film formation reaction while the remainder inserts into the carbon structure. The capacity due to the irreversible reaction is represented 于在碳材料表面形成了锂离子固体电解质界面层（SEI）。在这个过程中电池中的部分循环锂离子将会被消耗，而它形成的钝化层将会对电池的容量平衡产生深远的影响，因为它将会根据碳的使用类型去消耗很大部分的循环锂离子。？

如果电池中的锂离子逐渐减少，那得归因于电池体系内各种界面反应。在电池循环过程中，容量平衡是不可逆地变化，并且锂离子在两电极中嵌入深度也在改变，考虑到所有使用碳基电极的锂离子电池都存在初始碳钝化过程，电池最初是在放电状态下组装成的，包括未嵌锂的碳和最大锂量的金属氧化物活性电极。如图4所示则表示两电极中的锂离子数量，这说明了在焦炭/LiMn2O4电池体系中，前几次循环过程中，理想状态和实际情况有较大差异。

如图4a为理想的锂电池模型，在第一次充电过程中，所有从正极脱嵌的锂离子都将嵌入负极中，同样在首次放电过程中，所有的锂离子将会回嵌到正极材料中，然而在实际的电池体系中，在首次充电过程中，部分从正极脱嵌的锂离子将会用于不可逆的成膜反应，而余下的锂离子则会嵌入到碳结构中，如图4b下方的小方块则表示不可逆反应所消耗的容

schematically in Fig. 4b by the smaller box below the negative electrode. After the cell is finished charging to some arbitrary cutoff voltage, the positive electrode has been delithiated to the extent possible under the charging conditions and the negative electrode is as full of lithium as possible given the amount of positive electrode mass available. Ideally the lithium content in the carbon at this point is at its maximum safe value. Also, we can imagine that the passivation layer is fully formed on the initial charging cycle, having consumed a certain amount of cyclable lithium irreversibly.

When this cell is now discharged for the first time, the total quantity of lithium available for discharge is equal only to the amount of lithium reversibly inserted into the carbon electrode. Hence, the initial irreversible lithium lost cannot be recovered or utilized. The discharge proceeds until all of the reversible lithium is removed from the carbon electrode. At this time, the stoichiometry in the positive electrode will not reach its initial value upon cell assembly due to the capacity lost on the initial charging cycle. This situation is reflected in Fig. 4 in the bottom diagram. If the cell operates without any additional side reactions for the rest of its life, it will still never utilize the full range of stoichiometry available in the positive electrode. Thus for the above

carbon/LiMn

2O

4

system it is safe to cycle within

the limits of Δx = 0.61 (x varying from 0 to 0.61) and Δy = 0.83 (y varying from 0.17 to 1.0) as shown in Fig. 4. It should be remembered that these Δx and Δy values are cell and material specific. 量，当电池在任意的截止电压范围内完成充电后，在该充电条件下正极电极中的锂离子已经尽可能的脱嵌完成，负极电极则尽可能的嵌入正极提供的有效锂离子。理想情况下，此时碳负极的锂量处于最大值，同样我们可以认为钝化层是在初始循环过程中形成的，并且不可逆的消耗了一定数量的可循环锂离子。

当电池完成首次充电之后，那么可用于放电的总的锂量则相当于嵌入到碳负极的可逆容量，因此初始损失的不可逆锂离子将不能被回嵌或利用，放电过程则直到所有的可逆锂从碳负极中脱出为止，此时由于首次充电周期中容量的损失，正极电极的电化学计量比则无法达到其初始值。这种情况如图4中底部图表所示，如果在后续循环过程中，该电池没有任何额外的界面反应，它将不会利用到正极电极有效的全部化学计量比。因此，对于以上焦炭/LiMn2O4电池体系而言，如图4当Δx=0.61（x的范围为0~0.61）Δy=0.83（y 的范围为0.17~1）时，该电池将能安全地循环，需要强调的是此处的Δx和Δy值为电池和材料的特征值。

The range of stoichiometries accessed in the negative electrode in this example depends on the positive to negative mass ratio parameter γ. If the ideal value of yγhad been used to fabricate this example cell, the initial loss of lithium due to the irreversible passivation process would prevent the carbon electrode from being fully utilized to an extent that depended directly on the amount of irreversible capacity that the particular carbon electrode material exhibited. Rather than let this happen, the common procedure is to assemble cells having a greater than theoretical amount of positive-electrode mass, thus allowing for losses of cyclable lithium during operation by initially providing extra lithium. One method of providing the extra lithium without increasing the cathode mass is to use overlithiated manganese oxide (Li1+xMn2O4) spinel electrodes as proposed by Tarascon et al

此例子红负极电极使用化学计量范围取决于正负极质量比参数γ，如果按照理想的γ制备电池时，由于不可逆钝化过程中损失的锂将会防止碳电极被充分利用的程度？，而这个程度直接依赖于特定的碳电极材料表现出不可逆容量，为了避免这种情况的发生，一般方法是在装配电池时，加入超过理论质量的正极材料，为电池工作期间消耗的可循环锂提供额外的锂离子，另外可以通过合成富锂锰酸锂尖晶石材料（Li1+x Mn2O4），而不是增加材料质量来提供额外的锂离子，这种观点由Tarascon和Peramunage学

and Peramunage et al.

Even with side reactions and irreversible capacity losses, the desired mass ratio can still be calculated via a formula analogous to the above one, although we must now include in the negative electrode capacity an additive contribution due to the passivation process. Referring to this contribution as Cirr (mAh/g), the capacity balancing condition can be

expressed as

For example, in the case of a lithium-ion cell fabricated using a carbon (petroleum coke) negative electrode and a lithium manganese oxide spinel positive electrode, the actual mass ratio desired for optimum utilization of the two electrodes is about 14% larger than its theoretical value. This excess capacity is a measure of the amount of lithium needed to form a stable film over the electrode surfaces. The active mass ratio for the graphite/LiMn2O4 system is ca. 2.4-2.45. Smaller mass ratios will prevent full utilization of the negative electrode whereas larger mass ratios present a safety hazard because the negative electrode can be overcharged (more lithium is available to insert into the electrode than is desirable). Overall cell performance such as energy density is maximized at the optimum mass ratio only.

It should also be apparent that there is

a relationship between the expected overcharge and overdischarge processes and the cell's capacity balance. For example, in the case of the lithium manganese oxide spinel material discussed above, overcharge reactions involving solvent oxidation depend on the 者提出。

即便存在界面反应和不可逆容量的损失，但是我们仍然可以通过一个类似上面的公式来计算出所需的质量比，虽然我们必须将由钝化反应引起的负极容量的影响考虑在内。我们将这影响记为 C irr (mAh/g)，其容量平衡公式由以下表示：

例如，在使用碳（石油焦）

负电极和锂锰氧化物尖晶石正极组成锂离子电池的

体系下，

由两电极的最佳利用率所得到的实际质量比大约比其理论值多出14%。这种多余的容量是在电极表面形成稳定钝化膜所需要的锂量。对于石墨/LiMn 2O 4电池体系而言，最佳的活性物质质量比大约为 2.4-2.45。较小的质量比将阻碍负极的充分利用而较大的质量比将存在安全隐患因为负极会出现过

充现象

（电极将会嵌入超过设定的锂离子）

。整体电池的性能比如能量密度将会

在最佳质量比时达到最大值。

很明显，

预期的过充和过放过程与电池的容量平

衡息息相关，

例如，在前面讨论的尖晶石锂锰的氧化

物体系中，

包含溶剂氧化反应在内的过充反应取决于

正常循环条件下，正极充分

capability of the cell to fully oxidize the positive electrode during normal cycling conditions. For cells with high mass ratios, this may not be possible because the negative electrode becomes fully charged before allowing the positive to become fully charged (i.e., before complete removal of lithium from the positive). Overdischarge of high-mass-ratio cells will affect the negative electrode by emptying the carbon of lithium completely and then driving the negative electrode potential up to an undesirably high value. In other cases, the mass ratio may be lower than desired leading to overcharge of the positive electrode. For example, in the case of the coke/LiMn2O4 system, mass ratios higher than 2.1 can lead to overlithiation of the negative electrode during charge. Mass ratios lower than 2.1 will have less lithium available than needed and will thus result in overdischarge of the negative electrode with accompanying negative safety or performance consequences.

The carbon passivation process is the most common and well-studied example of a side reaction in the lithium-ion cell that will change the capacity balance. However, a number of other processes are also capable of having this effect. Any side reaction that either produces or consumes lithium ions or electrons will lead to a change in the cell's capacity balance, with the potential to impact negatively the cell's performance. In addition, once the capacity balance is changed from its desired state, the changes are generally irreversible and may accumulate over many cycles to generate a hazardous condition in the cell. Although difficult to quantify experimentally, it is straightforward to follow these effects using battery models and computer simulations under dynamic conditions if the relevant phenomena are included in the models. 氧化时电池的容量。当电池具有较大的质量比时，在正极的锂离子完全脱出之前，负极电极的锂离子嵌入已经达到饱和，高质量比电池的过放状态将会影响到负极电极，它会导致碳负极完全排空锂离子，从而使负极电动势超过预期值。在其它情况下，较低的质量比将会导致正极电极出现过充状态。比如在石墨/LiMn

2

O

4

电池体系中，当质量比大于2.1时，在充电过程中，负极电池将会出现富锂现象；当质量比小于2.1时，可逆的锂容量将会减少，并且导致负极电极出现过放状态，给电池的安全和性能带来负面影响。

在锂电池体系中，碳的钝化过程是一种正常现象，通常作为一种界面反应的例子进行研究，并且它会改变电池的容量平衡。然而，还有一些其他的反应过程也会给电池带来这种影响。任何产生或消耗锂离子或者电子的副反应均会影响到电池的容量平衡。同时会潜在的给电池的性能带来负面影响。进而，一旦容量平衡从它的期望状态改变，在此后的几个循环过程中，这些变化将会是不可逆的并且逐渐积累从而使整个电池处于危险状态。尽管很难进行实验验证，但如果相关现象被包含在电池模型中，我们可以通过电池模型和计算机模拟动态地跟踪这些界面反应过程。

Formation Cycles

Lithium-ion cells exhibit a sharp decay in capacity during the first few cycles. This period is known as the formation period during which cells are conditioned prior to use.It is generally desirable for the capacity decay observed after the formation period to be very small compared to the total cell capacity, after which the charge-discharge reactions are nearly 100% efficient. The sharp decay in capacity is due primarily to the solid electrolyte interface layer formation on the negative electrode. Passivation of the carbon electrode during the formation period and subsequent capacity loss are highly dependent on specific properties of the carbon in use, such as degree of crystallinity, surface area, pretreatments, and other synthesis and process details. After the first few cycles, the cell stabilizes and exhibits a constant capacity. The formation cycles are one of the critical steps in the manufacture of lithium-ion systems. For graphitic materials such as Osaka Gas mesocarbon micobeads (MCMB), the irreversible capacity is as low as 8 to 15%, whereas for hard carbons it can be as high as 50% of the reversible capacity.

Fong et al.demonstrated that irreversible reactions occur on carbon-based electrodes during the first discharge in carbonate-based electrolytes prior to the reversible insertion-deinsertion of lithium ions. These irreversible reactions are associated with electrolyte decomposition and cause the formation of a passivating film or solid electrolyte interface on the surface of the carbon. When all the available surface area is coated with a film of decomposition products, further reaction stops. In subsequent cycles, these cells exhibit excellent reversibility and can be cycled without capacity loss for many

化成循环

锂离子电池在前几个循环周期内会表现出容量急剧衰减现象。这一现象被称为电池在使用前的化成期。通常我们期望在电池的活化期内相对于电池总容量，衰减容量越小越好。此后循环周期内，电池的充放电效率接近100%。容量急剧衰减主要是由于在负极表面固体电解质层的形成。活化期碳电极钝化膜的形成和随后容量的衰减高度依赖于所使用碳负极的特性，例如结晶度、表面积、预处理。经历过前面几个循环周期之后，电池趋于稳定，容量基本恒定。活化期是锂电池系统制造的关键步骤之一。石墨材料如大阪气体的中间相碳微珠（MCMB），它的首次不可逆容量比例低至8%—15%，而硬碳的不可逆容量则高达50%。

Fong等学者表明不可逆反应发生在碳基材料上，并且该反应在首次放过程中电碳酸脂类电解液体系中发生，它是在锂离子进行脱嵌之前的。这些不可逆反应与电解液的分解有关，并且导致碳负极表面形成钝化膜或固体电解质界面层。当所有的有效表面积形成分解产物的钝化膜时，钝化反应将会停止。在后续循环过程中，该电池将会体现出优异的可逆性，同时在循环过程中不会出现容量衰减。

cycles. These authors first showed that the reversible insertion of lithium into graphitic carbons was possible as long as the proper passivating solvent was present. Gas evolution was observed by Gozdz et al. during the formation of the passivation layer on the carbon electrode during the first charge of a lithium-ion cell. The gas evolved correlated well with the irreversible capacity loss observed during the formation cycle. More details of carbon passivation in various solvent systems and the mechanisms of the passivation process are reviewed in later sections on electrolyte reduction and film formation.

The formation period is critical in lithium-ion battery manufacture because of its economic impact. First, it obligates manufacturers to invest in battery cycling stations to cycle cells several times before sending them to market, consuming both time and resources. Second, irreversible capacity consumed during the formation period is lost to

the battery, directly subtracting from the system's energy. Last, the formation period generates gases which under some conditions may need to be vented prior to further operation of the cell. Research efforts worldwide continue to generate very high capacity carbon electrode materials having high irreversible capacities. To utilize these materials in the most efficient manner requires a prepassivation

or prelithiation scheme not involving the sacrifice of a substantial quantity of the cyclable lithium available in the positive electrode. Although several research groups have been studying these processes and potential alternative approaches, there is no known solution for eliminating the formation period in an economically feasible manner. 这些学者表明当钝化膜形成时，可逆的锂离子可以嵌入进石墨碳负极结构中。Gozdz等学者最先发现产气机理。在锂电池首次充放电时期碳负极表面形成钝化膜过程中，气体产生的过程中观察到不可逆容量的损失，关于在各种电解液体系中碳钝化反应和钝化过程的机理的更多细节将在后面的电解液分解和成膜反应章节中介绍。

由于其效益的影响，在锂离子电池的生产过程中，形成周期是至关重要的。首先，在电池进入市场之前，它需要厂家通过电池循环站来对电池进行多次循环检测，这需要花费大量的时间和精力。第二，在形成期间消耗的不可逆容量损失的电池，直接从系统的能量中除去。最后，当电池进行进一步测试时，形成期产生的气体需要在一定条件下排泄完全。而今世界范围内的研究也在深入进行，已经研究出具有更高的碳电极材料，同时它还有较高的不可逆容量。为了更加有效的利用这些材料，我们需要一个钝化或锂化的方法，以便避免正电极大量可循环锂的消耗。虽然几个研究小组一直在研究这些过程和潜在的替代方法，然而至今仍然没有一个经济可行的方法去消除形成期的影响。

Overcharge Phenomena

Under conditions of overcharge, major capacity losses have been observed in all types of lithium-ion cells. The poor overcharge resistance of commercial lithium-ion cells and the safety issues that result from overcharge have led to tight control over charging and discharging of commercial cells using built-in electronic circuitry. The future application cf lithium-ion cells in new areas would be facilitated by advances in understanding and controlling overcharge. In particular the use of lithium-ion cells in multicell bipolar stacks requires a greater degree of overcharge tolerance due to the difficulty in achieving uniform utilization of all cells in series stacks.

Overcharge losses can be classified into three main types at present: (i) overcharge of coke and graphite-based negative electrodes, (ii) overcharge reactions for high-voltage positive electrodes, and (iii) overcharge/high-voltage electrolyte oxidation processes. These side reactions lead to loss of the active material and consumption of electrolyte,both of which can lead to capacity loss in the cell.

Overcharge of Coke and Graphite-Based

Negative Electrodes

During overcharge of lithium-ion cells, metallic lithium may be deposited on the negative electrode surface as the primary side reaction. This reaction is expected for cells with excess cyclable lithium due to either higher than desired initial mass ratio or lower than expected lithium losses during the formation period. The freshly deposited lithium covers the active surface area of the negative electrode leading to a loss of the cyclable lithium and consumption of

过充现象

当处于过充条件下时，所有类型的锂离子电池均会出现较大容量的损失。商业化锂电池的耐过充和安全问题表明过充性能将会导致商用锂电池需要内置电子电路来严格控制其充放电过程。未来关于锂离子电池在新的领域的应用需要在过充的理解和控制两方面做出突破。特别是在多模块锂离子电池的使用上需要更大程度的耐过充能力，因为需要所有模块的电池都达到统一利用是相当困难的。

目前，过充损失可以概括为以下三个主要类型（1）焦炭和石墨负极的过充反应（2）高电压下正极电极的过充反应（3）过充条件下，高压电解液的氧化过程。这些界面反应将会导致活性材料的损失和电解液的消耗，以上这两个现象均会导致电池容量的衰减。

焦炭和石墨基负极电极过

充反应

锂电池过充时，锂金属将作为主要的副反应沉积在负极电极表面。这种反应主要是为了形成额外的可循环锂，而它主要归因于在电池的活化期时高于预期的初始质量比和低于预期的锂离子损失。由于金属锂的活性较高，刚沉积在负电极表面的锂将会与电解液

供水管网余氯衰减模型探讨

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第27卷第11期2007年11月 环 境 科 学 学 报 Acta Scientiae C ircu mstanti a e V o.l 27,N o .11N ov .,2007 基金项目:饮用水处理与输配过程中铜管管材对水质的影响效应研究与评价(No .2004-2006) Supported by W aterQu alit y A ssess m en t -E ffect of Copper Pipes i n Dri nk i ngW ater T reat m ent and Trans m issi on Process es (No .2004-2006)作者简介:崔勇(1979)),男,硕士,E -ma i :l c u iyong_2078@https://www.wendangku.net/doc/1c14654959.html,;*通讯作者(责任作者),E -ma i :l j hqu@rcees .ac .cn Biography :CU I Yong (1979)),m al e ,E -m ai :l cu i yong_2078@163.co m;*Corres pondi ng author ,E-m ai:l j hqu @rcees .ac .cn 崔勇,曲久辉,乐林生,等.2007.铜管模拟输配系统中氯胺衰减过程与模拟[J].环境科学学报,27(11):1761-1766C u iY ,Qu J H,Le L S , et a l . 2007.M od eli ng d ecay of ch l ora m i nes residua l s by copper p i pe d istri bu ti on test loop s yste m [J ].Acta Scienti ae C i rcum stanti ae ,27(11):1761-1766 铜管模拟输配系统中氯胺衰减过程与模拟 崔勇1,3 ,曲久辉 1,* ,乐林生2,康兰英2,戴婕2,刘锐平1,黄怡2,付军1,雷鹏举1 , 王树江 3 1.中国科学院生态环境研究中心环境水质学国家重点实验室,北京100085 2.上海市北自来水有限公司,上海200086 3.长春工业大学,长春130012 收稿日期:2006-07-09 修回日期:2007-11-21 录用日期:2007-11-21 摘要:研究了氯胺在铜管模拟输配系统中的衰减过程,并利用一级反应动力学模型对氯胺衰减规律进行了模拟;考察了p H 、初始氯胺浓度等水质条件与流速等水力条件对氯胺衰减速率的影响.结果表明,p H 值是影响氯胺衰减速率与金属铜溶出的重要因素,p H 越低氯胺衰减越快;提高氯胺初始浓度可加快氯胺衰减速度,也可增加金属铜的溶出量;流速对氯胺衰减速率的影响不大.此外,衰减动力学过程模拟结果表明,采用一级反应动力学模型可以较好地拟合不同条件下的氯胺衰减规律,从而对于工程中不同条件下消毒剂浓度预测具有重要意义.关键词:氯胺;铜管;模拟输配系统;衰减动力学 文章编号:0253-2468(2007)11-1761-06 中图分类号:X131.2 文献标识码:A M odeli ng decay of chlora m i nes resi duals by copper pi pe distri buti on test l oop syste m C U I Yong 1,3 ,QU Jiuhu i 1,* ,LE Linsheng 2 ,KANG Lany ing 2 ,DA I Jie 2 ,LI U Ru i p i n g 1 ,HUANG Y i 2 ,F U Jun 1 ,LE I Peng j u n 1 ,WANG Shu ji a ng 3 1.State k ey Laboratory of E nvironm ental Aquatic Ch e m istry ,Research C enter for E co -Env i ronm ental Sciences ,C h i nes e A cade m y of S ci ences , Beijing 100085 2.ShanghaiW ater W orks Sh i b eiL i m i ted C o .,Shangha i200086 3.Changchun Un i versit y ofTechnol ogy ,Changchun 130012 R ecei ved 9July 2006; recei ved i n revised for m 21N ove mber 2007; a ccepted 21Nove m ber 2007 A bs tract :Copper p i pe d i s tri buti on test l oop syste m w as e m p l oyed to i nvesti gate t he ch l ora m i nes decay processes ,and first order k i neti c modelw as used t o fi t experi m en tal res u lts .The eff ect s of differen t factors ,i ncludi ng pH,i n iti al ch l ora m i nes concen tration and fl ow rate ,on ch l ora m i nes decay rates w ere i nvesti gated.pH s ho w s i m pact on chlora m i nes decay ,and t he l ow er pH lead s t o h i gher chlora m i nes decayi ng rates and m ore s i gn ifican t Cu rel ease fro m p i pelines .Ch l oram i n es d ecay obviously accelerat es at h i gher i n i ti al ch l ora m i nes con cen trati on and m ore Cu releas e i s accord i ngly observed.F l o w rates have no obv i ous effects on chlora m ines d ecay .F i rst order k i n eti c m odel fitw ellw it h ch l ora m i nes decay processes under d ifferent cond itions ,w h ic h cou l d be val uab le for ch l ora m i ne res i duals pred i cti on in engi neeri ng practi ce . K eywords :c h lora m i n es ;copper p i pe ;d i stri bu tion test l oop sys t e m s ;decayi ng k i n eti cs 1 引言(Introducti o n) 氯、氯胺以其能提供持续的消毒能力而成为饮用水后氯化消毒中使用最为广泛的消毒剂.后氯化 消毒不仅是为了灭活滤池出水中残留的微生物,更为重要的是抑制微生物在管网输配系统中再生长,并控制管壁生物膜的生成与生长,而保持输配系统中足够的消毒剂浓度水平是实现上述目的的关键.

锂离子电池容量衰减机理和界面反应研究

Capacity Fade Mechanisms and Side Reactions in Lithium-Ion Batteries Pankaj Arorat and Ralph E. White Center For Electrochemical Engineering, Department of Chemical Engineering, University of South Carolina,Columbia, South Carolina 29208, USA ABSTRACT The capacity of a lithium-ion battery decreases during cycling. This capacity loss or fade occurs due to several different mechanisms which are due to or are associated with unwanted side reactions that occur in these batteries. These reactions occur during overcharge or overdischarge and cause electrolyte decomposition, passive film formation, active material dissolution, and other phenomena. These capacity loss mechanisms are not included in the present lithium-ion battery mathematical models available in the open literature. Consequently, these models cannot be used to predict cell performance during cycling and under abuse conditions. This article presents a review of the current literature on capacity fade mechanisms and attempts to describe the information needed and the directions that may be taken to include these mechanisms in advanced lithium-ion battery models。锂离子电池容量衰减机 理和界面反应研究 作者：Pankaj Arorat and Ralph E. White 美国，南卡罗来纳29208，哥伦比亚，南卡罗来纳州大学，化工学院化工系 摘要 锂电池在循环过程中，其容量会逐渐衰减。而出现容量衰减主要归因于几个不同的机理，这些机理大多与电池内部的界面反应相关，这些反应持续性的发生在电池的充放电环节，并且引起电解液的分解、钝化膜的形成、活性材料的溶解等其它现象。关于容量衰减的机理在目前公开的锂离子电池数学模型的文献中并未加以阐述，因此在锂电池循环过程中和处于苛刻的条件下，我们无法通过模型来对锂电池的性能作出有效的预测。本篇文章将陈述容量衰减的机理，并且试着去解释其本质，为构建先进的锂电池模型指明方向。 lntroduction The typical lithium-ion cell(Fig. 1) is made up of a coke or graphite negative electrode, an electrolyte which serves as an ionic path between electrodes and separates the two materials, and a metal oxide (such as LiCoO2, LiMn2O4, or LiNiO2) positive electrode. This secondary (rechargeable) lithium-ion cell has been commercialized only 概论 传统的锂电池由碳或石墨负极材料、作为电极间的离子传输通道的电解液、金属氧化物（例如LiCoO2、LiMn2O4、LiNiO2）正极材料三部分组成，这种二次（可充电）电池已经商业化。依照这种原理制作的锂电池已

给水管网水质模型管壁余氯衰减系数校正_张土乔

第42卷第11期2008年11月 浙 江 大 学 学 报(工学版) Journal o f Zhejiang U niv ersity (Engineer ing Science) Vol.42No.11Nov.2008 收稿日期:2007-11-29. 浙江大学学报(工学版)网址:w w w.journals.z https://www.wendangku.net/doc/1c14654959.html,/eng 基金项目:国家自然科学基金资助项目(50078048);教育部新世纪优秀人才支持计划资助项目(NCE T -04-0525).作者简介:张土乔(1963-),男,浙江余姚人,教授,博导,从事市政工程教学科研工作.E -mail:ztq@https://www.wendangku.net/doc/1c14654959.html, DOI:10.3785/j.issn.1008-973X.2008.11.025 给水管网水质模型管壁余氯衰减系数校正 张土乔,王鸿翔,郭 帅 (浙江大学市政工程研究所,浙江杭州310027) 摘 要:针对给水管网水质模型中各管道管壁余氯衰减系数难以确定的问题,采用余氯衰减一阶反应模型以及拉格朗日时间驱动动态水质模型,以管网节点余氯浓度作为校正数据,建立了在多工况下管壁余氯衰减系数校正数学模型.提出了基于极大极小蚁群算法的管壁余氯衰减系数校正方法,将可视度与经验余氯衰减系数值相对应,选择最优蚂蚁进行信息素更新.为避免陷入局部最有解,将信息素值限定在一定范围内.在优化求解过程中采用国际通用水力水质模拟软件EPA N ET 2获得所需的校正数据.算例结果表明,在管网水力模型准确和节点流量已知的前提下,采用极大极小蚁群算法对管壁余氯衰减系数进行校正,能够使模型节点余氯浓度的计算值与测量值更好地吻合. 关键词:给水管网;管壁余氯衰减系数;校正;水质模型;极大极小蚁群算法 中图分类号:T U 991.33 文献标识码:A 文章编号:1008-973X(2008)11-1977-06 Chlorine wall decay coefficients calibration of water distribution quality model ZHANG T u -qiao,WANG H ong -xiang ,GU O Shuai (M unicip al E ngineer ing Resear ch I nstitute ,Zhej iang Univer sity ,H angz hou 310027,China) Abstract:Chlorine w all decay co efficients vary betw een pipes and can be determ ined indirectly fro m field measured concentration data.A general calibratio n model under m ult-i m ode to identify these parameters w as for mulated based on the simple first -order reaction of chlorine and the Lagr angian time -based appr oach of dynam ic w ater quality mo del.T he mult-i m ode model was analyzed to collect more node residual chlor ine data for calibration.Max -m in ant co lony sy stem algor ithm w as proposed to solve the calibration mo del that w as coupled w ith hydraulic and w ater quality sim ulation models using EPANET 2T oolkits.Only elitist ant w as allow ed to prov ide feedback mechanism by updating the trails and the trails w ere limited to an inter val betw een some m ax imum and m inimum possible values.Empirical co efficients w ere utilized co rresponding w ith lo cal heuristic function to impr ove the convergence of optimizatio n.Case study show ed that the chlo -r ine w all decay coefficients calibrated by the m ax -min ant co lony system alg orithm g ave perfect match be -tw een the actual and com puted node residual chlo rine v alues. Key words:w ater distributio n system;chlo rine w all decay coefficient;calibration;w ater quality model;max -min ant co lony system algor ithm 给水管网水质方面的研究近年来在方法和复杂性方面都取得了很大的进展[1-4] ,但是对水质模型准确性的研究,还没有引起足够的重视.这是因为水质 模型的准确运行不仅以校正后的水力模型为前提,还需要比较准确的水质模型输入参数,各管段管壁 余氯衰减系数就是重要参数之一[5-6].

锂离子电池正极材料硅酸锰锂的改性及容量衰减机理

罗明勇等：水蒸气等温吸附表征水泥基材料孔隙结构· 1409 ·第41卷第10期 DOI：10.7521/j.issn.0454-5648.2013.10.14 锂离子电池正极材料硅酸锰锂的改性及容量衰减机理 程琥1，高丹2，施志聪2 (1. 贵州师范大学化学与材料科学学院，贵州省功能材料化学重点实验室，贵阳 550001；2. 广州市香港科大 霍英东研究院，绿色产品和加工技术研究中心，广州 511458) 摘要：以醋酸锂、醋酸锰、醋酸镁、正硅酸四乙酯为原料，采用溶胶–凝胶法制备Li2Mn1–x Mg x SiO4/C正极材料。用X射线衍射和扫描电子显微镜表征材料的晶体结构和形貌。结果表明，掺杂10%Mg的Li2MnSiO4材料仍具有正交斜方结构。电化学测试结果表明：Mg掺杂能够提高Li2MnSiO4材料的比容量，在16.65mA/g电流密度下，Li2Mn1–x Mg x SiO4/C(x=0.1)材料的首次放电比容量为212mA?h/g。用X射线衍射和X射线光电子能谱研究了硅酸锰锂正极材料的容量衰减机理，其主要是由硅酸锰锂晶体结构退化引起的。 关键词：锂离子电池；正极材料；硅酸锰锂；硅酸盐；镁掺杂 中图分类号：O614 文献标志码：A 文章编号：0454–5648(2013)10–1409–06 网络出版时间：2013–09–24 18:23:01 网络出版地址：https://www.wendangku.net/doc/1c14654959.html,/kcms/detail/11.2310.TQ.20130924.1823.014.html Modification and Deterioration Mechanism of Lithium Manganese Silicate as Cathode Material for Lithium-ion Batteries CHENG Hu1，GAO Dan2，SHI Zhicong2 (1. School of Chemistry and Material Science, Key Lab for Functional Materials Chemistry of Guizhou Province, Guizhou Normal University, Guiyang 550001, China; 2. Center for Green Products and Processing Technologies, Guangzhou HKUST Fok Ying Tung Research Institute, Guangzhou 511458, China) Abstract: Li2Mn1–x Mg x SiO4/C cathode material for lithium-ion batteries was synthesized by a sol–gel method using LiCH3COO?2H2O, Mn(CH3COO)2?4H2O, Mg(CH3COO)2?4H2O, and Si(OC2H5)4 as starting materials under Ar/H2 atmosphere. The crystal structures and morphology of the as-prepared compounds were characterized by X-ray powder diffraction (XRD) and scanning electron mi-croscopy, respectively. The Li2MnSiO4 material maintains an orthorhombic structure with up to 10% (mass fraction) Mg doping on the Mn sites. The result obtained by electrochemical tests of the cathode materials reveals that Mg doping can improve the specific capacity of Li2MnSiO4. An initial specific discharge capacity of 212mAh/g can be achieved for the Li2Mn1–x Mg x SiO4/C (x=0.1) cathode material at a current density of 16.65mA/g. The deterioration mechanism was also discussed based on the results determined by XRD and X-ray photoelectronic spectroscopy. The poor capacity retention is mainly caused by the deterioration of the silicate crystal. Key words: lithium-ion batteries; cathode materials; lithium manganese silicate; silicates; magnesium doping 1 Introduction The lithium-ion batteries (LIBs) industry is developed with dominating applications in portable electronic de-vices.[1] Recent development on hybrid electric vehicles (HEVs) and electric vehicles (EVs) promotes low carbon transportation and energy and environmental require-ments.[2] However, the conventional cathode materials, i.e., LiCoO2, LiNiO2, LiMnO2 and their ternary systems, can not meet the requirements for automotive applications due to their unsafety and high cost.[6–8] Polyanion systems based on the olivine structure have attracted considerable attention since Goodenough and co-workers developed it as the cathode material for lithium-ion batteries.[9–12] 收稿日期：2013–03–28。修订日期：2013–05–09。 基金项目：国家自然科学基金(21176045)；贵州省科学技术基金(黔科合J字[2012]2284)。 第一作者：程琥(1977—)，男，副教授。 通信作者：施志聪(1975—)，男，副教授。Received date:2013–03–28. Revised date: 2013–05–09. First author: CHENG Hu (1977–), male, Associate Professor. E-mail: chenghu8802@https://www.wendangku.net/doc/1c14654959.html, Correspondent author: SHI Zhicong (1975–), male, Associate Professor. E-mail: zhicong@ust.hk 第41卷第10期2013年10月 硅酸盐学报 JOURNAL OF THE CHINESE CERAMIC SOCIETY Vol. 41，No. 10 October，2013

锂电池随使用而最大容量下降的原因

锂电池随着使用次数增加而最大容量下降 将分为内因和外因来说： 1.内因 （1）在电极方面，反复充放电使电极活性表面积减少，电流密度提高，极化增大；活性材料的结构发 生变化；活性颗粒的电接触变差，甚至脱落；电极材料(包括集流体)腐蚀； 现阶段常用电池负极为石墨，正极是LiCoO2，LiFePO4以及LiMn2O4等，电池放点初期电解液会在电 极表面形成一层SEI（固态电解质）膜，其成分主要是ROCO2Li（EC和PC环状碳酸酯还原产物）、ROCO2Li和ROLi（DEC和DMC等链状碳酸酯的还原产物）、Li2CO3（残余水和ROCO2Li反应产物），若用LiPF6时，残余的HF会与SEI中ROCO2Li，使SEI中主要是LiF和ROLi。 SEI是Li+导体，脱嵌锂时碳电极体积变化很小，但即使很小，其产生的内应力也会使负极破裂，暴露 出来新的碳表面再与溶剂反应形成新的SEI膜，这样就造成了锂离子和电解液的损耗，同时，正极材料 活性物质膨胀超过一定程度也会形成无法修复的永久性结构触损耗，这样正极和负极的不断损耗造成了 容量的不断衰减；再者，增加的SEI膜会造成界面的电阻层架，使电化学反应极化电位升高，造成电池 性能衰减 在电极中，随着充放电反应的进行，黏结剂的性能也会逐步下降，，黏结强度降低，使电极材料脱落； 铜箔和铝箔是常用的负极和正极集流体，两者都容易发生腐蚀，腐蚀产物聚集在集流体表面成膜，增加 内阻，铜离子还能形成枝晶，穿透隔膜，使电池失效。 （2）在电解质溶液方面，电解液或导电盐分解导致其电导率下降，分解物造成界面钝化； 锂离子电池液体电解质一般由溶质（如LiPF6、LiBF4、LiClO4等锂盐）、溶剂和特种添加剂构成。电 解质具有良好的离子导电性和电子绝缘性，在正负极之间起着输送离子传导电流的作用。锂离子电池在 第一次充放电、过充和过放时以及长期循环之后，电解质会发生降解作用，并伴有气体产生，气体的组 成较为复杂，还无法通过某种反应在电池内加以消除。随着电池充放电次数的增加。由于电极材料氧化 腐蚀会消耗掉一部分电解液，导致电解液缺乏，极片不能完全清润到电解液，从而电化学反应的不完全，使得电池容量达不到设计要求。 （3）隔膜阻塞或损坏，电池内部短路等 隔膜的作用是将电池正负极分开防止两极直接短路。在锂离子电池循环过程中，隔膜逐渐干涸失效是电 池早期性能衰退的一个重要原因。这主要是由于隔膜中电解液变干使溶液电阻增大，隔膜电化学稳定 性和机械性能，以及对电解质浸润性在反复充电过程中变差造成的。由于隔膜的干涸，电池的欧姆内阻 增大，导致放电不完全，电池反复受到大容量过充，电池容量无法回复到初始状态，大大降低了电池的 放电容量和使用寿命。 2.外因 （1）快速充放电 快速充电时，电流密度过大，负极严重极化,，锂的沉积会更明显，使在铜箔与碳类活性物质边界处的铜 箔脆化，极易产生裂缝。电芯自发卷绕受到固定空间的限制，铜箔无法自由伸展产生压力，在压力的作 用下，原有的裂缝扩散生长，因扩展空间不够，铜箔发生断裂。 （2）温度 在明显高于室温的情况下，有机电解质的热稳定性成为首先要考虑的问题，这全要包括有机电解质自身 热稳定性以及电极隋机电解质相互作用的热稳定性两个方面。一般认为，正极/有机电解质的反应对铿 离子电池安全性的影响是主要因素。因为正极、电解质的反应动力学非常快，故控制着整个电池耐热

最全最经典的电池容量衰减原因总结

最全最经典的锂离子电池容量衰减原因分析（附各原因专家分析） 0本质原因 锂离子电池在两个电极间发生嵌入反应时具有不同的嵌入能量，而为了得到电池的最佳性能，两个宿主电极的容量比应该保持一个平衡值。在锂离子电池中，容量平衡表示成为正极对负极的质量比，即： γ=m+/m-=ΔxC-/ΔyC+ 式中C指电极的理论库仑容量，Δx、Δy分别指嵌入负极及正极的锂离子的化学计量数。从上式可以看出，两极所需要的质量比依赖于两极相应的库仑容量及其各自可逆锂离子的数目。一般说来，较小的质量比导致负极材料的不完全利用；较大的质量比则可能由于负极被过充电而存在安全隐患。总之在最优化的质量比处，电池性能最佳。 对于理想的Li-ion电池系统，在其循环周期内容量平衡不发生改变，每次循环中的初始容量为一定值，然而实际上情况却复杂得多。任何能够产生或消耗锂离子或电子的副反应都可能导致电池容量平衡的改变，一旦电池的容量平衡状态发生改变，这种改变就是不可逆的，并且可以通过多次循环进行累积，对电池性能产生严重影响。 在锂离子电池中，除了锂离子脱嵌时发生的氧化还原反应外，还存在着大量的副反应，如电解液分解、活性物质溶解、金属锂沉积等，如图1所示。Arora等[3]将这些容量衰减的过程与半电池的放电曲线对照起来，使得我们可以清楚地看出电池工作时发生容量衰减的可能性及其原因，如图2所示。 一、过充电 1、石墨负极的过充反应： 电池在过充时，锂离子容易还原沉积在负极表面：Li＋＋e→Li（s），沉积的锂包覆在负极表面，阻塞了锂的嵌入。【电源网】【李伟善】【黄可龙】【阮艳莉】导致放电效率降低和容量损失，原因有： ①可循环锂量减少；【电源网】【李伟善】【阮艳莉】 ②沉积的金属锂与溶剂或支持电解质反应形成Li2CO3，LiF 或其他产物；【电源网】【李伟善】【阮艳莉】 ③金属锂通常形成于负极与隔膜之间，可能阻塞隔膜的孔隙增大电池内阻。 【电源网】【李伟善】【阮艳莉】 ④由于锂的性质很活泼，易与电解液反应而消耗电解液.从而导致放电效率降低和容量的损失。【黄可龙】 快速充电，电流密度过大，负极严重极化，锂的沉积会更加明显。这种情况容易发生在正极活性物相对于负极活性物过量的场合，【电源网】但是，在高充电率的情况下，即使正负极活性物的比例正常，也可能发生金属锂的沉积。【李伟善】 2、正极过充反应 当正极活性物相对于负极活性物比例过低时，容易发生正极过充电。【李伟善】 正极过充导致容量损失主要是由于电化学惰性物质（如Co3O4，Mn2O3 等）的产生，破坏了电极间的容量平衡，其容量损失是不可逆的。 （1）LiyCoO2： LiyCoO2→(1-y)/3[Co3O4＋O2(g)]＋yLiCoO2 y<0.4【电源网】【李伟善】【黄可龙】 同时正极材料在密封的锂离子电池中分解产生的氧气由于不存在再化合反应（如生成H2O）与电解液分解产生的可燃性气体同时积累，后果将不堪设想。【电源网】【黄可龙】 （2）λ-MnO2锂锰反应发生在锂锰氧化物完全脱锂的状态下： λ-MnO2→Mn2O3+O2(g)【李伟善】【黄可龙】 3、电解液在过充时氧化反应 当压高于4.5V 时电解液就会氧化生成不溶物（如Li2Co3）和气体，这些不溶物会堵塞在电极的微孔里面阻碍锂离子的迁移而造成循环过程中容量损失。【电源网】【黄可龙】【阮艳莉】 影响氧化速率因素： 正极材料表面积大小【电源网】【黄可龙】 集电体材料【电源网】【黄可龙】 所添加的导电剂（炭黑等）【电源网】【黄可龙】

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锂离子电池充放电机理的探索 及“锂亚原子”模型的建立 贵州航天电源科技有限公司张忠林杨玉光 摘要：锂离子电池的研究和发展一直都是以“摇椅理论”为指导，由于受该理论的影响，很多现象很难用传统的电化学理论进行解释。作者在生产实践中通过对一些现象的观察，并做了大量的试验和研究，提出“锂亚原子”的模型，并在此模型的基础上，对锂离子电池的充放电反应机理和一些现象用电化学理论进行了解释。 主题词：锂离子电池、反应机理、锂亚原子 一、前言 锂离子电池是在锂金属电池基础上发展起来的。由于锂金属电池在充放电时出现锂枝晶，刺破隔膜造成短路，出现爆炸等现象，这一问题长期困扰锂金属电池的发展，目前仍很难投入到民用市场。锂离子电池研究始于20世纪80年代，1991年首先由日本索尼公司推出了批量民用产品，由于其具有比能量高、体积小、重量轻、工作电压高、无记忆效应、无污染、自放电小等优点，受到市场欢迎，并迅速占领市场，广泛用于移动通讯、笔记本电脑、移动DVD、摄像机、数码相机、蓝牙耳机等便携式电子产品。目前主要产地集中在日本、中国和韩国，预计2004年全球需求量将达到10亿只。 由于锂离子电池从开始研究到现在才20多年时间，真正投入应用也只有十多年的时间，基础理论的研究还不是十分成熟，对锂离子电池的生产和发展很难起到全面指导作用，特别是对电池充放电反应机理的认识还存在很大分歧，有些现象用目前的理论和机理还很难解释。本文对锂离子电池充放电反应机理提出了一些看法，并对生产中存在的现象进行了解释，希望与锂电池同行共同探讨。二、基本原理 目前锂离子电池公认的基本原理为“摇椅理论”，该理论认为锂离子电池充放电反应机理不是通过传统氧化还原反应来实现电子转移，而是通过锂离子在层状物质的晶格中嵌入和脱出，发生能量变化。