【作者】 李磊；

【导师】 张庶；

【作者基本信息】 电子科技大学 ， 材料科学与工程， 2023， 硕士

【摘要】 锂/氟化碳（Li/CF_x）电池因具有现有一次电池中最高理论能量密度（2180 Wh/kg）被广泛应用航空航天、电子设备、医疗器械等领域。电解液作为电池的重要组成部分,直接参与电化学过程中的离子传输和界面反应,对电池的倍率性能、放电容量以及工作温度范围等方面都起到了至关重要的作用。为解决Li/CF_x电池倍率性能差、工作温度窄的问题、进一步提升电池的放电性能,本文从电解液角度出发,研究分析不同金属阳离子和共溶剂对电池电化学性能的影响和作用机理;同时对适用于高温域下的电池体系进行了探索。具体研究内容如下:首先,采用锂、钠、钾离子电解液作为Li/CF_x电池电解液,对比分析相同体系下锂、钠、钾离子电解液对电池性能的影响。通过XRD、SEM、Raman等表征技术获得放电前后正极材料的结构形貌变化并分析钾离子电解液对电池性能的促进机制。实验结果表明钠、钾离子电解液均能有效地增强电池的倍率性能,钾离子电解液的作用效果最为明显,5 C放电倍率下放电容量提高了26.8%,达到515.44mAh/g。K⁺与F^-低的结合能以及KF低的溶解度可降低反应势垒,利于KF的成核;同时钾离子电解液高的离子扩散系数有助于电池实现更好的倍率性能。综上可知,界面反应及离子扩散等动力学过程是提升电池性能的关键。其次,在上述电解液体系中引入FEC共溶剂,研究FEC共溶剂对提升Li/CF_x电池能量密度有效性的同时分析总结不同体积占比的FEC对电池性能的影响。结果表明,FEC的加入能有效地提高电池放电能量密度,体积占比为10%时的提升效果最为明显,0.1 C下能量密度分别提高了11.4%、15.8%以及9.7%,这得益于FEC在放电过程中被还原分解,在提供部分容量的同时改善界面、降低反应电阻。此外,在Li/CF_1.05及Li/GEF_1.0电池体系中的应用证实了FEC提升效果的普适性。最后,为拓宽Li/CF_x电池的工作温度范围,开发了双盐（LiBF₄+LiDFOB）电解液体系。研究表明,向LiBF₄基电解液中加入LiDFOB能很好地提高电解液的热稳定性,改善电池高温性能,在150℃下、0.1 C,放电容量为1062.4 mAh/g。在此基础上加入低粘度的共溶剂以增强电极电解液浸润性,提高电池的室温性能,0.1 C下放电容量提高了11.9%,为775.3 mAh/g。更多还原

【Abstract】 Li/CF_x batteries are widely used in aerospace,electronic devices,and medical devices because they have the highest theoretical energy density（2180 Wh/kg）among existing primary batteries.The electrolyte,as an important part of the battery,is directly involved in the ion transport and interfacial reactions in the electrochemical process,and plays a crucial role in rate performance,discharge capacity and operating temperature range of the battery.To solve the problems of poor rate performance and narrow operating temperature of Li/CF_x battery and further improve the discharge performance of the battery,this thesis studied the effects and mechanisms of different metal cations and co-solvents on the electrochemical performance of the battery from the perspective of electrolytes.Meanwhile,the battery system applicable to the high temperature domain was explored.The main research contents are as follows:Firstly,lithium,sodium and potassium ion electrolytes were used as Li/CF_x battery electrolytes,and the effects of lithium,sodium and potassium ion electrolytes on battery performance under the same system were compared and analyzed.The structural and morphological changes of the cathode material before and after discharge were obtained by XRD,SEM,Raman and other characterization techniques.The promoting mechanism of potassium ion electrolyte on battery performance was analyzed.The study found that sodium and potassium ion electrolytes can effectively enhance the rate performance of the battery,which the potassium ion electrolyte showed the most obvious effect,and the discharge capacity was increased by 26.8%with 515.44 mAh/g at the discharge rate of 5C.The low binding energy of K⁺and F^-and the low solubility of KF can reduce the reaction barrier and facilitate the nucleation of KF;meanwhile,the high ion diffusion coefficient of potassium ion electrolyte helps the battery to achieve better rate performance.In summary,it can be seen that the kinetic processes such as interfacial reaction and ion diffusion are the key to enhance the performance of batteries.Secondly,FEC co-solvent was added to the above electrolyte system to study the effectiveness of FEC co-solvent on improving the energy density of Li/CF_x battery while analyzing and summarizing the effects of different volume ratios of FEC on the electrochemical performance of the battery.The results show that FEC can effectively increase the battery discharge energy density,and the most obvious enhancement is achieved at 10%of FEC volume ratio,with 11.4%,15.8%and 9.7%increase in energy density at 0.1 C,respectively.This is due to the fact that FEC is reduced and decomposed during discharge,improving the interface and reducing the reaction resistance while providing partial capacity.In addition,the application in Li/CF_1.05 and Li/GEF_1.0 batteries has confirmed the universality of the FEC improvement effect.Finally,a double salt（LiBF₄+LiDFOB）electrolyte system was developed to broaden the operating temperature range of Li/CFx batteries.It was shown that the addition of LiDFOB to the LiBF₄-based electrolyte can well improve the thermal stability of the electrolyte and improve the high temperature performance of the battery,with a discharge capacity of 1062.4 mAh/g at 150℃and 0.1 C.On this basis,a low viscosity co-solvent was added to enhance the wettability between electrode and electrolyte and improve the room temperature performance of the batteries,with 11.9%increase in capacity to 775.3mAh/g at 0.1 C.更多还原