The lithium/carbon monofluoride (Li/CFx) battery was one of the first lithium/solid cathode systems to be used commercially.1 Its theoretical specific energy is about 2180 Wh/kg and is among the highest for the solid cathode systems. The open-circuit voltage is 3.2 V with an operating voltage of 2.5–2.9 V. Its practical specific energy and energy density range from 250 Wh/kg and 635 Wh/L for smaller cells to 590 Wh/kg and 1050 Wh/L for larger sizes. Because of the relatively high cost of CFx compared to other solid cathodes such as manganese dioxide, its use is currently restricted to specialized applications such as biomedical and military, where its superior technical characteristics are required. The active components of the cell are lithium for the anode and carbon monofluoride (CFx) for the cathode where x is typically in the range 0.9–1.1 for commercial products. CFx is synthesized by the reaction of fluorine gas with carbon powder at a high temperature (HT). CFx is electrochemically active and stable up to 400°C, producing a cathode that resists self-discharge, resulting in a long shelf life for the Li/CFx cell. Typically, the electrolyte consists of lithium tetrafluoroborate (LiBF4) in gamma-butyrolactone or lithium hexafluoroarsenate (LiAsF6) in a mixture of propylene carbonate and dimethoxyethane. The simplified version of the discharge process is shown by the following reactions Anode:xLi=Li++xe−Cathode:CFx+xe−=xC+xF−Overallreaction:CFx+xLi=xLiF+xC The carbon monofluoride is converted into carbon, which is more conductive than CFx, thereby lowering the cell’s internal resistance, improving the voltage regulation and cell efficiency while the LiF precipitates in the cathode structure. Recent studies2,3 have shown that subfluorinated CFx (0.33< x < 0.66) materials exhibit a higher rate capability up to 25°C and an improved low temperature performance down to −40°C compared to a commercial CFx prepared from coke with x = 1.08. In practice, Li/CFx is a primary battery system in which lithium metal serves as the anode against a fluorinated graphite cathode in the presence of an electrolyte. Upon discharge, lithium is oxidized while fluorine is reduced, producing elemental carbon and LiF, which precipitates on the remaining CFx structure. Certain facts about the mechanism of discharge of this system are known, such as the increase in electrical conductivity, attributable to the formation of conductive graphite from CFx that occurs as the battery is discharged.4 However, the structure of the CFx cathode during and after discharge, the mechanism of the defluorination process, and the exact location and form of the LiF remain unresolved. The primary objective of this study is to investigate the three types of fluorinated graphite materials to determine any chemical and structural distinctions between the starting materials, and as they undergo lithiation. Electrochemical studies on these different types of CFx have indicated significant differences in electrochemical performance. Ultimately, the aim is to correlate these findings with electrochemical data collected on the same materials to better understand the discharge mechanisms. The three starting CF materials were CFx F, which is fiber based; CFx G, which is graphite based, and CFx C, which is petroleum coke based. These three compounds are of nominally the same composition, i.e., (CF)x, x ~ 1, but result from different preparation routes. Each starting compound was subjected to a chemical reduction in n-butyllithium (nBL) under identical conditions to achieve several levels of lithiation followed by 19F and 13C NMR analyses. Both the solid powders and the liquid filtrates were studied. Though it is appreciated that chemical lithiation is only a relatively crude model for electrochemical reduction, in part because of the very rapid, highly exothermic, and far-from-equilibrium nature of the reaction compared to relatively slow discharge rates characteristic of CFx cells, it does provide a useful means to characterize the samples in a timely manner. Therefore, although the spectroscopic details may somewhat differ between chemically and electrochemically reduced samples, it is expected that the main reaction species and the trends observed in their formation would be similar. The reactants were added very slowly, in a titration-like fashion, to allow the reaction to proceed uniformly, and the chemical reaction was closely monitored for drastic changes in temperature.

中文翻译：

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化学锂化 CF[sub x] 的固态核磁共振研究

锂/一氟化碳 (Li/CFx) 电池是最早投入商业使用的锂/固体阴极系统之一。1 其理论比能量约为 2180 Wh/kg，是固体阴极系统中最高的。开路电压为 3.2 V，工作电压为 2.5-2.9 V。其实际比能量和能量密度范围从小型电池的 250 Wh/kg 和 635 Wh/L 到小型电池的 590 Wh/kg 和 1050 Wh/L更大的尺寸。由于与二氧化锰等其他固体阴极相比，CFx 的成本相对较高，因此其使用目前仅限于需要其卓越技术特性的专业应用，如生物医学和军事。电池的活性成分是阳极的锂和阴极的一氟化碳 (CFx)，其中 x 通常在 0.9-1 的范围内。1 用于商业产品。CFx 是通过氟气与碳粉在高温 (HT) 下反应合成的。CFx 在高达 400°C 的温度下具有电化学活性和稳定性，可产生抗自放电的阴极，从而延长 Li/CFx 电池的保质期。通常，电解质由γ-丁内酯中的四氟硼酸锂 (LiBF4) 或碳酸丙烯酯和二甲氧基乙烷的混合物中的六氟砷酸锂 (LiAsF6) 组成。放电过程的简化版本由以下反应显示 阳极：xLi=Li++xe−Cathode:CFx+xe−=xC+xF−Overallreaction:CFx+xLi=xLiF+xC 一氟化碳转化为碳，它比CFx更导电，从而降低电池的内阻，提高电压调节和电池效率，而 LiF 在阴极结构中沉淀。最近的研究 2,3 表明，与由焦炭制备的商用 CFx 相比，低氟化 CFx (0.33< x < 0.66) 材料在高达 25°C 的温度下具有更高的倍率性能，并且在低至 -40°C 的低温下性能有所改善，x = 1.08. 在实践中，Li/CFx 是一种原电池系统，其中在电解质存在的情况下，锂金属作为阳极对氟化石墨阴极。放电时，锂被氧化，而氟被还原，产生元素碳和 LiF，它们沉淀在剩余的 CFx 结构上。关于该系统放电机制的某些事实是已知的，例如电导率的增加，这归因于电池放电时 CFx 形成导电石墨。4 然而，放电期间和放电后 CFx 阴极的结构、脱氟过程的机制以及 LiF 的确切位置和形式仍未解决。本研究的主要目的是研究三种类型的氟化石墨材料，以确定起始材料之间的任何化学和结构差异，以及它们在锂化过程中的差异。对这些不同类型 CFx 的电化学研究表明电化学性能存在显着差异。最终，目的是将这些发现与在相同材料上收集的电化学数据相关联，以更好地了解放电机制。三种起始 CF 材料是 CFx F，它是基于纤维的；CFx G, 它是石墨基的，CFx C 是石油焦基的。这三种化合物名义上具有相同的组成，即(CF)x，x ~ 1，但产生于不同的制备途径。每种起始化合物在相同条件下在正丁基锂 (nBL) 中进行化学还原，以实现多种锂化水平，然后进行 19 F 和 13 C NMR 分析。研究了固体粉末和液体滤液。尽管化学锂化只是电化学还原的一个相对粗糙的模型，部分原因是与 CFx 电池的放电速率相对较慢的特性相比，该反应具有非常快速、高度放热和远离平衡的性质。确实提供了一种有用的方法来及时表征样品。所以，尽管化学还原和电化学还原样品的光谱细节可能有所不同，但预计主要反应物质及其形成过程中观察到的趋势是相似的。以滴定方式非常缓慢地加入反应物，以使反应均匀进行，并密切监测化学反应的温度是否发生剧烈变化。