富鋰三元正極材料Li-Ni-Mn-Al-O的改性研究與形貌調(diào)控
發(fā)布時間：2018-11-10 11:48
【摘要】：鋰離子電池由于其高能量密度已被廣泛使用作為電子產(chǎn)品,電動車以及混合動力車的儲能裝置。富鋰三元層狀正極材料Li-Co-Ni-Mn-O具有較高的放電比容量和熱力學(xué)穩(wěn)定性,然而Co的價格,毒害問題等一定程度上會限制該種材料的實(shí)際應(yīng)用。與其他的有害且價格昂貴的金屬元素不同,Al是一種環(huán)境友好且廉價的元素,Al的摻雜可以在NCM的表面形成Li+傳輸?shù)耐ǖ?這將有益于鋰離子的擴(kuò)散。此外,Al的存在提升了材料中Mn3+的比率,這增大了材料的電子傳輸能力。同時,Al的存在可以降低材料的放電活化能并且延緩材料SEI膜的生成速率。此外,Al替代Co可以提升材料的循環(huán)性能和材料的熱穩(wěn)定性。因而Al替換Co制備的Li-Ni-Mn-Al-O富鋰正極材料的性能是值得期待的。本試驗(yàn)采用溶膠凝膠法對Li-Ni-Mn-Al-O正極材料進(jìn)行了比例優(yōu)化,Li1.2Ni0.3Mn0.6Al0.1O2.2材料的性能最優(yōu)。在優(yōu)化過程中發(fā)現(xiàn),Li含量低于最優(yōu)化值時材料中存在尖晶石相,隨著Li含量提升尖晶石相含量逐漸降低。材料達(dá)到最優(yōu)Li含量后,進(jìn)一步富鋰,多余的Li會形成Li2O而使材料團(tuán)聚,從而導(dǎo)致材料的性能下降。當(dāng)材料中的Mn主要以四價態(tài)形式存在時,材料的性能最優(yōu)。這為其他研究者設(shè)計(jì)材料提供了一個依據(jù)。為了提升材料的倍率性能和循環(huán)穩(wěn)定性,分別對材料進(jìn)行Fe替代Ni和Cu O包覆處理。Fe替代Ni直接降低了材料中的Ni含量,達(dá)到降低材料陽離子混排程度的目的,提升了材料的倍率性能。但過多的Fe替代會降低材料的放電比容量。對材料進(jìn)行少量的Cu O包覆可以改善材料的循環(huán)穩(wěn)定性,并且提升材料的倍率性能,但會犧牲材料的放電比容量。對材料的形貌進(jìn)行調(diào)控,是一種有效的提升材料性能的方法。分別采用靜電紡絲法,水熱法和固相法制備不同形貌的材料。采用靜電紡絲法可以制備扁絲狀前驅(qū)體,但高溫會對絲狀結(jié)構(gòu)造成破壞。采用水熱法可以制備出片層堆疊結(jié)構(gòu)的材料。此材料的循環(huán)穩(wěn)定性和倍率性能要明顯優(yōu)于溶膠凝膠材料,30次循環(huán)之后材料的放電比容量為199.86m Ah/g,在1000m A/g充放電電流密度下,放電比容量可以達(dá)到101.35m Ah/g。采用固相法可以得到球殼結(jié)構(gòu)的材料。但由于固相法制備材料的不均勻性材料的性能較差。對水熱法得到的材料的工藝進(jìn)行進(jìn)一步的優(yōu)化,優(yōu)化條件包括聚乙烯吡咯烷酮(PVP)用量,進(jìn)樣速率和煅燒溫度。發(fā)現(xiàn)隨著PVP使用量的增加,材料由層狀堆疊的結(jié)構(gòu)逐漸變?yōu)閱蝹�小顆粒結(jié)構(gòu)。隨著進(jìn)樣速率的增加,材料也是由層狀堆疊的結(jié)構(gòu)逐漸變?yōu)閱蝹�小顆粒結(jié)構(gòu)。測試發(fā)現(xiàn)小顆粒的材料富鋰化程度很低。提升材料的燒結(jié)溫度,發(fā)現(xiàn)材料的晶型逐漸向大塊晶體結(jié)構(gòu)轉(zhuǎn)變,降低了材料的性能。最優(yōu)化的工藝條件為,2gPVP用量,10ml/h的進(jìn)樣速率,750℃的煅燒溫度。將水熱法優(yōu)化后的層狀堆疊材料(HT-NMA)與溶膠凝膠材料制備的片狀材料(SG-NMA)進(jìn)行比較。HT-NMA材料之間接觸更加充分。采用BET模型對數(shù)據(jù)進(jìn)行擬合,HT-NMA的比表面積為8.92m2/g而SG-NMA的比表面積為5.90m2/g,大的比表面積使得HT-NMA與導(dǎo)電劑混合更加充分,會具有更好的電子傳導(dǎo)能力。在20m A/g的電流密度下循環(huán)30圈,HT-NMA的容量保持率為86%,在1000m A/g的電流密度下HT-NMA的放電比容量為108m Ah/g。通過將Nyquist圖和Bode圖協(xié)同分析,發(fā)現(xiàn)相比于SG-NMA,HT-NMA具有更小的電子傳遞電阻,并且5次循環(huán)后,其高頻弧增長的幅度更小。對于這兩種材料,相比于SEI電阻,材料的電子傳遞電阻對材料的電化學(xué)性能具有更大的影響。循環(huán)前后良好的電子傳遞電阻是層狀堆疊材料性能優(yōu)異的原因。
[Abstract]:As a result of its high energy density, the lithium ion battery has been widely used as an energy storage device for electronic products, electric vehicles and hybrid vehicles. Li-Co-Ni-Mn-O with Li-Co-Ni-Mn-O has high discharge specific capacity and thermodynamic stability. However, the price of Co, the problem of poisoning and so on will limit the practical application of the material. Unlike other harmful and expensive metal elements, Al is an environment-friendly and inexpensive element, and the doping of Al can form a Li + transmission channel on the surface of the NCM, which will benefit the diffusion of lithium ions. In addition, the presence of Al increases the ratio of Mn3 + in the material, which increases the electron transport capacity of the material. At the same time, the presence of Al can reduce the discharge activation energy of the material and delay the generation rate of the material SEI film. In addition, the Al substitution Co can improve the cycle performance of the material and the thermal stability of the material. Therefore, the performance of the Li-Ni-Mn-Al-O-rich anode material prepared by the Al replacement Co is expected. The performance of Li-Ni-Mn-Al-O cathode material was optimized by sol-gel method, and Li1. 2Ni0. 3Mn0. 6Al0. 1O2. In the optimization process, the spinel phase is present in the material when the Li content is lower than the optimum value, and the content of the spinel phase increases with the content of Li. After the material has reached the optimum Li content, the lithium is further enriched, and the excess Li forms Li2O and the material is agglomerated, resulting in a decrease in the performance of the material. When the Mn in the material is mainly in the form of a tetravalent state, the performance of the material is optimal. This provides a basis for other investigator design materials. In order to improve the rate and cycle stability of the material, Fe was used to replace Ni and Cu O. and the Fe substitution Ni directly reduces the Ni content in the material, so that the purpose of reducing the cation mixing degree of the material is achieved, and the rate performance of the material is improved. However, excessive Fe substitution can reduce the discharge specific capacity of the material. a small amount of cu o-coating of the material can improve the cycle stability of the material and increase the rate performance of the material, but the discharge specific capacity of the material is sacrificed. The method for controlling the morphology of the material is an effective method for improving the performance of the material. The materials of different shapes were prepared by electrostatic spinning, hydrothermal method and solid phase method, respectively. The flat-filament precursor can be prepared by the electrospinning method, but the high temperature can cause damage to the filamentous structure. the material of the sheet stacking structure can be prepared by adopting a water thermal method. The cycle stability and the rate performance of this material are obviously superior to that of the sol-gel material. The discharge specific capacity of the material after 30 cycles is 1996.86m Ah/ g, and the discharge specific capacity can reach 101.35m Ah/ g at the charge-discharge current density of 1000m A/ g. and the material of the spherical shell structure can be obtained by adopting a solid-phase method. but the performance of the non-uniform material of the material is poor due to the solid phase method. The process of the material obtained by the hydrothermal method is further optimized, and the optimization conditions include the amount of the polynorbornene (PVP), the sample rate and the burn-in temperature. it has been found that as the amount of pvp is increased, the material gradually becomes a single small particle structure from the structure of the layered stack. As the sample rate increases, the material is also gradually changed from the structure of the layered stack to a single small particle structure. the test found that the material with the small particles had a low level of lithium-rich. the sintering temperature of the material is increased, and the crystal type of the material is found to gradually change to the bulk crystal structure, and the property of the material is reduced. The optimized process conditions were, for example, an amount of 2gPVP, a sample rate of 10 ml/ h, a burn-in temperature of 750. degree. C. The layered stack material (HT-NMA), which was optimized by hydrothermal method, was compared to a sheet material (SG-NMA) made of a sol-gel material. the contact between the ht-nma materials is more sufficient. The specific surface area of the HT-NMA is 8.9m2/ g and the specific surface area of the SG-NMA is 5.90m2/ g, and the specific surface area of the HT-NMA is 5.90m2/ g. The capacity retention of HT-NMA was 86% at the current density of 20 m A/ g, and the discharge specific capacity of HT-NMA at the current density of 1000m A/ g was 108m Ah/ g. It is found that HT-NMA has a smaller electron transfer resistance than SG-NMA and HT-NMA, and the increase of high-frequency arc is smaller after 5 cycles. For both materials, the electron transfer resistance of the material has a greater effect on the electrochemical performance of the material compared to the SEI resistance. The good electron transfer resistance before and after the cycle is the cause of the excellent performance of the layered stacked material.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TM912
[Abstract]:As a result of its high energy density, the lithium ion battery has been widely used as an energy storage device for electronic products, electric vehicles and hybrid vehicles. Li-Co-Ni-Mn-O with Li-Co-Ni-Mn-O has high discharge specific capacity and thermodynamic stability. However, the price of Co, the problem of poisoning and so on will limit the practical application of the material. Unlike other harmful and expensive metal elements, Al is an environment-friendly and inexpensive element, and the doping of Al can form a Li + transmission channel on the surface of the NCM, which will benefit the diffusion of lithium ions. In addition, the presence of Al increases the ratio of Mn3 + in the material, which increases the electron transport capacity of the material. At the same time, the presence of Al can reduce the discharge activation energy of the material and delay the generation rate of the material SEI film. In addition, the Al substitution Co can improve the cycle performance of the material and the thermal stability of the material. Therefore, the performance of the Li-Ni-Mn-Al-O-rich anode material prepared by the Al replacement Co is expected. The performance of Li-Ni-Mn-Al-O cathode material was optimized by sol-gel method, and Li1. 2Ni0. 3Mn0. 6Al0. 1O2. In the optimization process, the spinel phase is present in the material when the Li content is lower than the optimum value, and the content of the spinel phase increases with the content of Li. After the material has reached the optimum Li content, the lithium is further enriched, and the excess Li forms Li2O and the material is agglomerated, resulting in a decrease in the performance of the material. When the Mn in the material is mainly in the form of a tetravalent state, the performance of the material is optimal. This provides a basis for other investigator design materials. In order to improve the rate and cycle stability of the material, Fe was used to replace Ni and Cu O. and the Fe substitution Ni directly reduces the Ni content in the material, so that the purpose of reducing the cation mixing degree of the material is achieved, and the rate performance of the material is improved. However, excessive Fe substitution can reduce the discharge specific capacity of the material. a small amount of cu o-coating of the material can improve the cycle stability of the material and increase the rate performance of the material, but the discharge specific capacity of the material is sacrificed. The method for controlling the morphology of the material is an effective method for improving the performance of the material. The materials of different shapes were prepared by electrostatic spinning, hydrothermal method and solid phase method, respectively. The flat-filament precursor can be prepared by the electrospinning method, but the high temperature can cause damage to the filamentous structure. the material of the sheet stacking structure can be prepared by adopting a water thermal method. The cycle stability and the rate performance of this material are obviously superior to that of the sol-gel material. The discharge specific capacity of the material after 30 cycles is 1996.86m Ah/ g, and the discharge specific capacity can reach 101.35m Ah/ g at the charge-discharge current density of 1000m A/ g. and the material of the spherical shell structure can be obtained by adopting a solid-phase method. but the performance of the non-uniform material of the material is poor due to the solid phase method. The process of the material obtained by the hydrothermal method is further optimized, and the optimization conditions include the amount of the polynorbornene (PVP), the sample rate and the burn-in temperature. it has been found that as the amount of pvp is increased, the material gradually becomes a single small particle structure from the structure of the layered stack. As the sample rate increases, the material is also gradually changed from the structure of the layered stack to a single small particle structure. the test found that the material with the small particles had a low level of lithium-rich. the sintering temperature of the material is increased, and the crystal type of the material is found to gradually change to the bulk crystal structure, and the property of the material is reduced. The optimized process conditions were, for example, an amount of 2gPVP, a sample rate of 10 ml/ h, a burn-in temperature of 750. degree. C. The layered stack material (HT-NMA), which was optimized by hydrothermal method, was compared to a sheet material (SG-NMA) made of a sol-gel material. the contact between the ht-nma materials is more sufficient. The specific surface area of the HT-NMA is 8.9m2/ g and the specific surface area of the SG-NMA is 5.90m2/ g, and the specific surface area of the HT-NMA is 5.90m2/ g. The capacity retention of HT-NMA was 86% at the current density of 20 m A/ g, and the discharge specific capacity of HT-NMA at the current density of 1000m A/ g was 108m Ah/ g. It is found that HT-NMA has a smaller electron transfer resistance than SG-NMA and HT-NMA, and the increase of high-frequency arc is smaller after 5 cycles. For both materials, the electron transfer resistance of the material has a greater effect on the electrochemical performance of the material compared to the SEI resistance. The good electron transfer resistance before and after the cycle is the cause of the excellent performance of the layered stacked material.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TM912
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