Porous Hollow Carbon@Sulfur Composites for High-Power Lithium-Sulfur Batteries
Porous Hollow Carbon@Sulfur Composites for High-Power Lithium-Sulfur Batteries
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DOI：
10.1002/anie.201100637
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发表时间：
2011-01-01
影响因子：
16.6
通讯作者：
Archer, Lynden A.
中科院分区：
文献类型：
--
作者：
Jayaprakash, N.;Shen, J.;Archer, Lynden A.
在二次锂电池的阴极材料中，元素硫具有最高的理论容量，相对于锂为1672 mA hg/m2，这至少是商业上使用的过渡金属磷酸盐和氧化物的十倍。作为阴极，硫以非拓扑方式容纳两个锂离子，支持电化学氧化还原反应16Li + S8O8Li2S。[1]使用硫作为电池的阴极材料的其他优点是其成本低且广泛可用;其固有的过度充电保护机制，这提高了电池的安全性;宽的工作温度范围;以及长寿命周期的潜力。[2，3]因此，硫作为阴极材料被广泛研究，并被认为是电动和混合动力汽车的有前途的候选材料。[4]尽管有这种前景，但用于高功率应用的Li-S二次电池系统的实现一直存在问题。由于硫固有的不良导电性（在258 ℃下为5 × 10 - 30 S cm-3）和充电过程中高阶多硫化物的穿梭，商业上可行的Li-S电池尚未实现。[4]硫的低电导率限制了活性材料的利用，因为材料内的电化学接触不良。穿梭是一种循环过程，其中在充电期间在阴极处产生的长链多硫化锂（Li2Sn，2 <n <8）溶解到电解质中并迁移到阳极，在阳极处它们以寄生方式与锂电极反应以产生低级多硫化物，低级多硫化物扩散回到硫阴极并再生高级形式的多硫化物。[5]这种穿梭过程是由多硫化物的浓度梯度驱动的，有文献报告表明它为锂硫电池的过充电保护提供了潜在的好处。[6]然而，如果不加以控制，则会导致放电期间总活性材料质量的利用率降低，引发电流泄漏，循环性能差，以及电池的库仑效率降低。[7]在过去的三十年里，世界各地的研究团队已经深入研究了防止锂硫二次电池中多硫化物溶解和穿梭的方法。一系列研究集中在定制电解质以抑制多硫化物溶解。例如，基于THF、THF/甲苯和二氧戊环的电解质已被报道在低放电电流（0.01 mAcm2）下促进硫的利用，[8]这对应于两个月的放电。已经报道了基于三氟甲磺酸锂在四甘醇二甲醚中的电解质制剂在控制Li-S电池中的穿梭中是有效的，但是具有不可接受的48%的低效率。[9]室温离子液体由于其不燃性、不挥发性、宽电化学窗口以及热稳定性和化学稳定性，最近作为Li-S电池的电解质引起了人们的关注。[10]不幸的是，Li金属电极处的高界面阻抗限制了Li-S电池的倍率性能和长期循环寿命。[11]保护锂阳极[12]和降低电解质中多硫化物阴离子的迁移率[13]的持续努力也被证明在提高Li-S电池的循环寿命和容量衰减方面基本无效。[14]另一种方法是利用涂有导电聚合物的复合硫粉末来防止穿梭。这种方法已经引起了极大的兴趣，因为导电聚合物的某些性质，包括它们的形态和电化学稳定性，已经被证明可以产生稳定的复合材料，其在低（100mAg Ω 1）电流速率下50次循环后产生的容量范围为500和800 mA Ω 1。[15...
Among cathode materials for secondary lithium batteries, elemental sulfur has the highest theoretical capacity, 1672 mA hg À1 against lithium, which is at least ten times greater than that of commercially used transition-metal phosphates and oxides. As a cathode, sulfur hosts two lithium ions non-topotactically, supporting the electrochemical redox reaction 16 Li+ S8Q8 Li2S.[1] Other advantages of using sulfur as the cathode material for batteries are its low cost and widespread availability; its intrinsic protection mechanism from overcharging, which enhances battery safety; a wide operating temperature range; and the potential for a long life cycle.[2, 3] Sulfur has consequently been studied extensively as a cathode material and is considered a promising candidate for electric and hybrid electric vehicles.[4] Despite this promise, implementation of Li–S secondary battery systems for high power applications has been problematic. Hindered by the inherent poor electrical conductivity of sulfur (5 10À30 S cmÀ1 at 258C) and shuttling of higher-order polysulfides during charging, a commercially viable Li–S cell is yet to be realized.[4] Sulfur s low electrical conductivity limits active material utilization as a result of poor electrochemical contacts within the material. Shuttling is a cyclic process in which long-chain lithium polysulfides,(Li2Sn, 2< n< 8), generated at the cathode during charging, dissolve into the electrolyte and migrate to the anode where they react with the lithium electrode in a parasitic fashion to generate lower-order polysulfides, which diffuse back to the sulfur cathode and regenerate the higher forms of polysulfide.[5] This shuttling process is driven by the concentration gradient of polysulfide and there are literature reports which suggest that it provides a potential benefit for overcharge protection in Li–S batteries.[6] However, left unchecked, it leads to decreased utilization of the overall active material mass during discharge, triggers current leakage, poor cycleabilty, and reduced columbic efficiency of the battery.[7] Over the last three decades, methods for preventing polysulfide dissolution and shuttling in Li–S secondary batteries have been intensively investigated by research teams world-wide. One line of study focuses on tailoring the electrolyte to restrain polysulfide dissolution. Electrolytes based on THF, THF/toluene and dioxolane, for example, have been reported to facilitate utilization of sulfur at low discharge currents (0.01 mAcmÀ2),[8] which corresponds to a two-month discharge. An electrolyte formulation based on lithium triflate in tetraglyme has been reported to be effective in controlling shuttling in Li–S batteries, but with an unacceptably low efficiency of 48%.[9] Room temperature ionic liquids have recently attracted attention as electrolytes for Li–S batteries due to their nonflammability, nonvolatility, wide electrochemical window, and thermal and chemical stabilities.[10] Unfortunately, high interfacial impedance at the Li metal electrode limits the rate capability and long-term cycle life of the Li–S batteries.[11] Persistent efforts to safeguard the lithium anode [12] and to reduce mobility of the polysulfide anions in the electrolyte [13] have also proven largely ineffective in enhancing the cycle life and capacity fading in Li–S batteries.[14]An alternative method utilizes composite sulfur powder coated with conducting polymers to prevent shuttling. This approach has attracted significant interest as certain properties of conducting polymers, including their morphology and electrochemical stability, have been shown to produce stable composites, which yield capacities ranging from 500 and 800 mA hÀ1 after 50 cycles at low (100mAgÀ1) current rates.[15 …