本文選題：鋰硫電池　切入點(diǎn)：自放電特性　出處：《青島科技大學(xué)》2017年碩士論文

【摘要】：鋰硫電池是目前已知采用固態(tài)材料為活性物質(zhì)的比能量最高的二次電池體系。然而,多硫化物穿梭效應(yīng)導(dǎo)致的容量衰減快、庫(kù)侖效率低、自放電率高及產(chǎn)熱等問(wèn)題限制了鋰硫電池的實(shí)用化進(jìn)程。本文通過(guò)對(duì)鋰硫軟包電池的放電深度(DOD),環(huán)境溫度,擱置時(shí)間及放電倍率等因素進(jìn)行控制,測(cè)試并分析電池自放電特性、產(chǎn)熱特性及內(nèi)阻特性等外特性及其規(guī)律,并進(jìn)一步通過(guò)原位四電極法分析了電池循環(huán)過(guò)程中內(nèi)部電解液電導(dǎo)率變化情況,探究影響鋰硫電池特性的影響因素和相關(guān)機(jī)制。實(shí)驗(yàn)結(jié)果表明,鋰硫電池的自放電特性和其電化學(xué)反應(yīng)機(jī)制與過(guò)程產(chǎn)物密切相關(guān)。未循環(huán)過(guò)的鋰硫電池因其沒(méi)有生成多硫化物而幾乎沒(méi)有自放電行為,已循環(huán)過(guò)的鋰硫電池在不同的放電深度下具有不同的自放電特性。在放電深度(DOD)為0時(shí),自放電最大,隨著放電深度增加,自放電率不斷減小直到低電壓平臺(tái)處自放電較為平穩(wěn),并在放電末尾處自放電最小。此外,自放電與環(huán)境溫度、擱置時(shí)間皆呈正相關(guān)性。在低溫及放電末尾處貯存已循環(huán)過(guò)的鋰硫電池受自放電行為的影響更小。對(duì)鋰硫電池充放電產(chǎn)熱特性研究結(jié)果表明:在大電流充放電時(shí),表面不同位置會(huì)產(chǎn)生不同程度的溫度變化,電池靠近極耳的中上部區(qū)域較開(kāi)始時(shí)溫升最大;隨著循環(huán)次數(shù)增多、環(huán)境溫度降低、充放電電流增大,電池的最大溫升變大;在一次循環(huán)中,前期循環(huán)時(shí)放電時(shí)溫升較大,最易出現(xiàn)最大溫升處為DOD30%階段,隨著循環(huán)次數(shù)增多,充電溫升超過(guò)放電溫升,充電結(jié)束時(shí)成最大溫升處;在一定溫度范圍內(nèi),較高溫度對(duì)電池的熱穩(wěn)定性有積極作用,隨著溫度的升高,此時(shí)電池內(nèi)部極化小,充電時(shí)最大溫升更穩(wěn)定。通過(guò)階躍法和阻抗法測(cè)試了鋰硫電池內(nèi)阻特性,對(duì)比發(fā)現(xiàn)鋰硫電池內(nèi)阻變化規(guī)律與電池表面溫度的變化規(guī)律有很好的吻合度,電池內(nèi)阻的增加或降低直接影響電池溫度的變化。原位四電極法測(cè)試研究發(fā)現(xiàn),電池內(nèi)部電解液阻抗放電時(shí)隨著放電深度的增加而增加,在30%DOD時(shí)達(dá)到最高值,此階段對(duì)應(yīng)于高價(jià)態(tài)多硫化物的生成以及向低價(jià)態(tài)多硫化物的轉(zhuǎn)化,電解液中多硫化物濃度不斷增加并達(dá)到最高值。當(dāng)繼續(xù)放電時(shí)之后阻抗降低;對(duì)應(yīng)于低價(jià)態(tài)多硫化物向Li2S2和Li2S的轉(zhuǎn)化,可溶性多硫化物的濃度不斷降低。隨著循環(huán)次數(shù)的增多,在相同DOD條件下電解液的阻抗增加,作者認(rèn)為在循環(huán)過(guò)程中電解液溶劑被消耗,以及多硫化物的不可逆溶解導(dǎo)致電池電解液阻抗的增加。
[Abstract]:Lithium-sulfur batteries are known to use solid materials as active substances with the highest specific energy of the secondary battery system.However, the problems such as fast capacity attenuation, low Coulomb efficiency, high self-discharge rate and heat production due to polysulfide shuttle effect limit the practical process of lithium-sulfur batteries.In this paper, the discharge depth, ambient temperature, shelving time and discharge rate of lithium-sulfur soft-clad battery are controlled, and the characteristics of self-discharge, heat generation and internal resistance of the battery are tested and analyzed.Furthermore, the change of electrolyte conductivity during battery cycle was analyzed by in situ four-electrode method, and the influencing factors and related mechanisms were explored.The experimental results show that the self-discharge characteristics and electrochemical reaction mechanism of lithium-sulfur batteries are closely related to the process products.The uncirculated lithium-sulfur battery has almost no self-discharge behavior because it does not produce polysulfide. The circulating lithium-sulfur battery has different self-discharge characteristics at different discharge depths.When the discharge depth (DOD) is 0, the self-discharge is maximum. With the increase of discharge depth, the self-discharge rate decreases continuously until the self-discharge at the low voltage platform is more stable, and the self-discharge at the end of the discharge is the smallest.In addition, self-discharge is positively correlated with ambient temperature and shelving time.At low temperature and at the end of discharge, the effect of self discharge behavior on the storage of circulating lithium sulfur batteries is less than that at the end of discharge.The results of the study on the thermal characteristics of lithium-sulfur battery show that when the charge and discharge are high, the temperature changes in different positions of the surface will be different, and the temperature rise in the middle and upper part of the battery near the polar ear will be the highest at the beginning, and with the increase of cycle times,The maximum temperature rise of the battery increases with the decrease of ambient temperature and the increase of charge / discharge current. In the first cycle, the maximum temperature rise during the early cycle is larger, and the maximum temperature rise is at the DOD 30% stage, with the increase of the cycle times.The temperature rise of charge exceeds the temperature of discharge and becomes the maximum temperature rise at the end of charging. In a certain temperature range, higher temperature has a positive effect on the thermal stability of the battery. With the increase of temperature, the internal polarization of the battery is small.Maximum temperature rise during charging is more stable.The internal resistance characteristics of lithium-sulfur battery were measured by step method and impedance method. It was found that the variation of internal resistance of lithium-sulfur battery was in good agreement with the change of cell surface temperature, and the increase or decrease of internal resistance of battery directly affected the change of battery temperature.In situ four-electrode method, it was found that the impedance discharge of electrolyte increased with the increase of discharge depth and reached the highest value at 30%DOD, which corresponds to the formation of high-valence polysulfide and the transition to low-valence polysulfide.The concentration of polysulfide in electrolyte is increasing and reaching the highest value.When the discharge continues, the impedance decreases, and the concentration of soluble polysulfide decreases continuously, corresponding to the conversion of low valence polysulfide to Li2S2 and Li2S.With the increase of the number of cycles, the impedance of the electrolyte increases under the same DOD conditions. The authors believe that the electrolyte solvent is consumed during the cycle and the irreversible dissolution of polysulfide leads to the increase of the impedance of the electrolyte.
【學(xué)位授予單位】：青島科技大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TM912

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