锂离子电池体系：
锂离子电池是一个能够给新兴得移动设备提供能量得技术。这个技术的进展已经有很多精彩的综述。整个电池体系中没有金属锂存在。锂只是以锂离子存在于溶液中，当它嵌入碳负极或者正极材料中的时候，才以原子态存在。能够嵌入锂的碳材料，取代了金属锂电池负极，使得电池的循环性能得到延展。SONY公司在Tazawa和Nagaura描述了锂离子电池的结构和性能后不就就将其商品化。 Asahi化工在开发这个技术上有同样的成就。Besenhard发现了元素的电化学嵌入碳和石墨，Basu将其应用到二次电池中。Goodenough等发现了用于所有锂离子电池的可逆锂钴氧化物、锂锰氧化物和镍氧化物。一个二次电池体系的容量{dy}次达到了一次电池的水平。锰和钴电池的电池反应为：

Li₀C + LiCoO₂ === Li_xC + Li_1-xCoO₂
Li₀C + LiMn₂O₄ === Li_xC + Li_1-xMn₂O₄

锂离子电池在放电状态下装配。负极中的锂来源于正极。电池的{dy}次充电将锂从正极转移到负极。虽然现在锂锰氧化物和锂镍氧化物也在工业上使用，但锂钴氧化物才是目前{zj0}的正极材料。钴材料可以提供145mAh/g的工作容量，可以通过掺杂Al、Mg等来增加结构的稳定性，避免析氧反应。混和氧化物锂镍钴氧化物有190mAh的更高容量，并且比纯的镍氧化物更稳定。锰电池的电压为3.7V比钴电池的3.6V要高，但是容量较低，只有115mAh。锰氧化物更廉价更稳定，但是它对电解质六氟磷酸锂和残余的水水解生成的HF非常敏感。锂离子电池，特别是廉价的锰氧化物电池，正在将它们开发为电动和混和动力车辆电源，达到90Ah以上容量。SAFT在欧洲已经为大型锂离子电池取得了空间电源的资格。
除了钴和锰材料以外，锂离子和钒、磷酸盐等材料正应用在聚合物锂离子电池中。这意味着低成本、长寿命、高稳定性、xxx。这些材料放电电压稍低，只有3.4V但是容量达到可观的140mAh/g接近钴氧化物。
商业锂离子电池主要使用石墨或者硬碳材料。Dahn对各种锂离子电池的碳负极材料做了专门的综述。硬碳（煤炭）能够提供长的循环寿命，但是容量较低，只有270mAh/g，并且化成时候的容量损失要比石墨大。在充满状态下，所有的碳材料和锂的可逆电位的差都在50mV以内。新型的高容量锡合金和锂钴氮化物负极材料正在开发中，在这个电压下能够提供700mAh的容量。

和锂一次电池一样，在锂离子电池首次充电的过程中，负极上自然地会生成SEI层。一旦形成，这个薄膜层能够阻隔溶液和聚合物更多地和碳化物负极反应。形成SEI层是电池稳定性能最关键的步骤。SEI层的组成是一个非常值得研究的课题。目前，对纯净、干净的锂表面的研究已经相当多地揭示了SEI层在形成过程中的组成。除去杂质后，所有的实验都在高真空下进行，反应产物用红外光谱分析。常见的环状和链状的有机碳酸盐电解质溶质反应生成相应的锂羟基化合物。
高的电池电压限制了有机电解质溶剂的选择。一般，对锂和4.5V（vs Li）氧化电位稳定的环状和链状的有机碳酸脂是理想的选择。溶质中，六氟磷酸锂高导电率使得它比四氟硼酸锂要受到重视，溶剂一般是环状有机碳酸脂（乙烯基碳酸脂等）和链状有机碳酸脂（二甲基碳酸脂、二乙基碳酸脂、甲基乙基碳酸脂等等）的混合物。每个制造商有它自己的电解质配方。
丙稀碳酸脂不能和石墨负极同时使用，因为它在充电的时候能够嵌入到石墨负极中。两种新的溶质在发展中，用以取代六氟磷酸锂，以xx它水解出HF的影响。 Oestand 等用两个烃基官能团取代了六氟磷酸根中的氟原子，以获得更好的稳定性。另外一种是锂二乙二酸硼酸脂（LiBOB）。这是一种需要确定溶剂才能提供好的性能的盐。

电解液添加剂，如亚乙烯碳酸脂能够形成稳定膜，使得在形成SEI的时候锂的消耗量减少并延长电池的存放寿命。其他添加剂能够作为安全量度物质xx电流中断设备（CID）。这些化合物含有叔氢原子，例如环己基苯和联苯碳酸脂，它们是电化学活性物质，能够在4.5V(vs Li/Li+)左右产生氢气。如果电池在超过4.2V的电压下过充，一旦电压达到4.5V，这些化合物就能够反应产生氢气。内部气体压力迅速增加将xxCID将电池和滥用环境断开。
图四展示了典型的锂离子电池的结构。所有的电池生产商都将安全设备合在一起，如阻断隔膜、压力孔、CID和正温度系数（PTC）电阻等在滥用条件下保护电池避免短路。另外，电子电源控制系统和安全线路在电池工作时会测量温度、电流和电压。所有的生产商都坚持要求电池工作的温度、电压。电流都在控制范围内以使电池处于安全范围内，并且避免活性物质受到损害。锂离子电池如果不在受控范围内工作，将会自我损坏。
锂离子电池采用薄的微孔聚烯烃隔膜，通常是达到50％孔率的聚乙烯。这些小孔直径大约在400埃。在隔膜温度达到约110摄氏度的时候，这些孔能够闭合，使得电池内阻突然增大，停止电池反应（术语称为断路隔膜）。电池外壳为镀镍钢，但现在薄且轻的铝壳来减轻重量。
安全是锂离子电池的最重要的问题。商业电池都要通过UL实验室、UN和DOT运输规则等安全测试。每个电池中都有上述设备保护并且和电子电源管理器一起打包在每个电池中，用来抵抗外部的恶劣条件。在电池的内部安全设计中，电解液的活性也是一个重要的因素。当电解液自发地直接和正极、负极的活性物质反应能够吸收电池的热量。正、负极材料和电解液之间的反应活性决定了散热条件。这些反应大约在130摄氏度开始发生，以破坏正极的SEI层为起始。这些反应能够很快自动地散热，但是电池本身也被破坏了。电池内部短路或者至于高温下可能达到这样的温度。

原文：

Lithium ion battery system:

The Li-ion battery is an enabling technology for a new generation of portable electronic devices. There are several excellent reviews of the technology and its development. There is no lithium metal in the battery. Lithium is found only in ionic form in solution and in an atomic state when intercalated into the carbon anode or the oxide cathode materials. A carbon, capable of intercalating lithium, replaced the metallic lithium anode that has defied cycling for any extended period. Sony first commercialized the Li-ion system shortly after the publication by Tazawa and Nagaura who described the first commercial cell, its construction, and its performance. Asahi Chemical also made an effort to develop the technology. The elements of electrochemical intercalation into carbons and graphites was established by Besenhard and used in a rechargeable cell by Basu. Goodenough et al. established the reversible lithiation of cobalt, manganese, and nickel oxides that are used in all Li-ion cells. For the first time, the energy storage capability of a rechargeable system approached that of the primary battery systems. The cell reactions for manganese and cobalt cathodes are :

Li₀C + LiCoO₂ === Li_xC + Li_1-xCoO₂
Li₀C + LiMn₂O₄ === Li_xC + Li_1-xMn₂O₄

The Li-ion cells are assembled in the discharged state. The source of lithium for the anode is the cathode. The first charge of the cell transfers lithium from the cathode to the anode. Lithium cobalt oxide is the active cathode material of choice although lithium manganese spinel and lithium nickel oxide are being used. The cobalt material delivers about a 145 mAh/g working capacity and may be doped with Al, Mg, etc., to stabilize its structure against oxygen evolution. The mixed oxide LiNi_0.8Co_0.2O₂ has a higher capacity (about 190 mAh/g) and is more stable than the pure nickel oxide. The manganese cell discharges at a higher voltage (3.7 V vs. 3.6 V for cobalt) but has a lower capacity (about 115 mAh/g). The manganese is lower in cost and is more stable against oxygen evolution but is susceptible to acid leaching by HF produced from the hydrolysis of residual water in the LiPF₆ electrolyte. Li-ion cells, especially those with low cost manganese cathodes, are being developed and used for electric and hybrid vehicles with capacities of 90 Ah or more. Large Li-ion cells have been space-qualified by SAFT in Europe.

 In addition to cobalt and manganese materials, lithium iron and vanadium phosphates are now used as cathode materials in commercial Li-ion polymer cells. These offer the possibility of lower cost, while providing greater stability for longer life and safety.104-106 The materials discharge at a lower voltage (3.4 V) but have a reasonable capacity (140 mAh/g) near that for the cobalt compounds. Commercial Li-ion batteries mainly use graphite or hard carbon materials. Dahn reviewed the various carbon anode materials for use in Li-ion batteries. Hard carbons (cokes) have a longer cycle life but lower capacity (about 270 mAh/g) and higher first cycle loss than do graphites. When fully charged, all carbon materials approach to within 50 mV from the reversible lithium potential. New higher capacity tin alloy and lithium cobalt nitride based anodes are under development with the potential of reaching over 700 mAh/g useful capacity.

Just as with lithium metal batteries, the solid electrolyte interface (SEI) layer forms spontaneously on the carbonaceous anode of a Li-ion cell during first charge. Once formed, the film protects the solvent and polymers from further reaction with the carbon lithium anode. This film formation is the key element to stable battery performance. The composition of the SEI film has been the subject of considerable speculation. Recently, studies on pure, clean, lithium surfaces have shed considerable light on the composition of the SEI layer during its formation. To eliminate contamination, all experiments were carried out in high vacuum and the reaction products were identified by infrared spectral analysis. The common cyclic and linear organic carbonate electrolyte solvents react to form the corresponding lithium alkoxides. The high cell voltage restricts the choice of organic solvents for the electrolyte. Generally, cyclic and linear carbonates are the materials of choice as they are stable to reduction by lithium and against oxidation to above 4.5 V vs. Li. In the electrolyte, LiPF₆ is preferred as the salt for its higher conductivity over LiBF4 , and a solvent combination of a cyclic carbonate (ethylene carbonate, etc.) coupled with linear carbonate materials (dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, etc.). Each manufacturer has its own preferred electrolyte composition.

 Propylene carbonate cannot be used with graphitic anodes as it intercalates into the anodes on charge. Two new solutes are under development to replace the LiPF₆ and eliminate HF formation from hydrolysis. Oestand et al. have substituted two alky groups for two of the fluorine atoms in PF₆ ^- for better stability. The other is lithium bisoxalatoborate (LiBOB). This salt requires reformulation of the solvent composition for good performance. Electrolyte additives such as vinylene carbonate form stable films that reduce the amount of lithium used in the SEI formation and improve storage life. Other additives are added as a safety measure to activate the current interrupt devices (CID) device. These compounds have a tertiary hydrogen atom, such as cyclohexyl benzene and biphenylcarbonate, are electroactive, and generate hydrogen gas around 4.5 V vs. Li/Li1. If a cell should be overcharged above the normal 4.2V charge voltage, when the cell voltage reaches 4.5 V, the compound reacts to generate hydrogen gas. The internal gas pressure increases rapidly to activate the CID and disconnect the cell from this abusive condition. Typical Li-ion cell constructions are shown in Fig. 4. The designs of all cell manufacturers incorporate safety devices such as shutdown separators, pressure vents, CIDs and positive temperature coefficient (PTC) resistors to protect against abuse conditions from external shorts.

In addition, electronic power management and safety circuitry measures temperature, current, and voltage during cell operation. All manufacturers insist on temperature, voltage, and current control to limit cell operation within safe bounds and to avoid damage to the active materials. Li-ion cells have the capability to self-destruct if the operation is not controlled. The Li-ion cell design employs a thin microporous polyolefin separator, usually polyethylene, of the order of 50% porosity. The pores are about 400 Å in diameter. The pores close up to increase internal cell resistance and stop cell action when the separator reaches about 110°C (termed a shut-down separator). The cell case is nickel-plated steel but thin lightweight aluminum cans are used to reduce the weight. Safety is a key issue with the Li-ion cell system. Cells for commercial use are required to pass safety testing programs such as that of the UL Laboratories and the UN and DOT shipping regulations.

The cells are protected against external abuse by the devices described above along with the electronic power management units incorporated in all battery packs. While a good part of safety resides in the internal cell design, the reactivity of the electrolyte also plays a role. Thermal runaway in Li-ion batteries occurs when the electrolyte spontaneously reacts directly with the active cathode and anode materials. Reactivity with anode and cathode active materials with the electrolyte determines the onset of thermal runaway conditions. These reactions initiate at about 130°C and start with the destruction of the SEI layer on the anode. The reactions are autocatalytic and quickly send the cell into thermal runaway where it self destructs. Temperatures in this range can result from internal cell shorts or exposure to high temperature environments.       

- 作者： 访问统计：　2005年05月30日, 星期一 09:55