【作者】 张帅；

【导师】 慈立杰；

【作者基本信息】 哈尔滨工业大学 ， 材料科学与工程， 2023， 硕士

【摘要】 随着新能源汽车行业的迅速发展,用户对高能量密度、高效安全动力电池的产品要求也在日益增长。由于锂金属负极的理论比容量高达3860 m Ah/g,被人们看作提高了电池能量密度的“圣杯”。但同时它也容易产生锂枝晶、死锂,而且库伦效率会随循环的进行逐渐降低,体积膨胀也变得愈发严重,因此增加了锂金属电池短路的风险并阻碍了其实用化。三维结构化锂金属负极能够有效地控制锂金属的体积变化、抑制枝晶生长,在实用化方面更具优势。锂硅合金从化学成分角度对锂金属进行改性,能够降低锂金属的化学活性,使其更稳定。针对碳纤维布（CC）的憎锂性,本文通过使用良导电的氮掺杂氧化锌修饰三维碳纤维布（N-Zn O/CC）,构建了亲锂的碳纤维宿主并在4秒内快速吸附熔融状态下的锂金属,从而制备出碳布基锂金属复合负极（N-Zn O/CC@Li）。这种负极所组装的对称电池电荷转移阻抗仅为24Ω,并且在电流为1 m A/cm²,面容量为1 m Ah/cm²的条件下能够以11 m V的极化电压稳定运行超3000小时,其形核过电位仅为9.0 m V,相较于单纯使用氧化锌制备的复合锂金属负极（Zn O/CC@Li）仅运行400小时而言,性能优势明显。而且匹配磷酸铁锂（LFP）正极时,N-Zn O/CC@Li|LFP全电池在0.2C的倍率下循环100圈后容量保持率仍有93.03%。为了进一步提高复合锂负极的实用性,通过在熔融锂的过程中添加3 wt%的硅粉作为第二相,形成锂硅合金(Li₂₂Si₅)。再利用N-Zn O/CC吸附制备出基于锂硅合金的三维锂金属负极(N-Zn O/CC@Li-Si_{3 wt%}),其组装的对称电池电荷转移阻抗仅为0.4Ω,相较于吸附纯锂金属降低了一个数量级,而且在电流为3 m A/cm²,面容量为1 m Ah/cm²的条件下能够以15 m V的极化电压稳定运行超过900小时。当进行极限电流条件测试后,发现N-Zn O/CC@Li-Si_{3 wt%}复合负极能够在电流为10 m A/cm²,面容量为10 m Ah/cm²的条件下仍能够稳定运行。当匹配磷酸铁锂（LFP）正极组装全电池进行倍率测试,发现其在20C下仍保持39.4 m Ah/g的较高放电容量,相较于纯锂金属有近两倍的提升。在匹配商用LFP正极（面负载量约为14 mg/cm²）时,0.5C的倍率下循环150圈后仍有98.4m Ah/g的放电比容量,容量保持率为66.96%,比纯锂负极循环寿命提高近8倍。综上,利用氮掺杂氧化锌对碳纤维布进行改性能够有效地提高其亲锂性,良导电的氮掺杂氧化锌能够显著的降低复合锂金属负极的电荷转移阻抗。这种构建良导电亲锂三维骨架的策略可以为无宿主的锂金属提供稳定的结构,不仅能够实现引导锂金属的均匀沉积、抑制锂枝晶生长,还能够有效的防止锂金属的体积膨胀与结构塌陷。进一步,通过对锂金属进行化学成分的改性,引入微量硅作为第二相构成具有良好流动性的锂硅合金,并将其灌入到亲锂碳纤维布中从而形成协同效应,最终通过匹配不同面负载量的磷酸铁锂正极,验证了这种锂硅合金复合三维锂负极具有良好的实际应用潜力,这种研究策略为锂金属的实用化研究提供了有效的思路。更多还原

【Abstract】 With the rapid development of new energy vehicle,the requirements of users for power batteries with high energy density,efficiency and safety are also growing.Since the theoretical specific capacity of lithium metal anode(LMA)is up to 3860m Ah/g,it is considered as the"Holy Grail"to improve the battery energy density.But at the same time,it is also easy to produce lithium dendrites and dead lithium.And the coulombic efficiency will gradually decrease,and the volume expansion will become more serious during cycling,thus increasing the risk of short circuit of lithium metal batteries and hindering its commercialization.The three-dimensional structured LMA can effectively inhibit its’volume expansion and control the dendrites,which is better to apply;the Li-Si alloy can modify the chemical composition of lithium metal,which can reduce the chemical activity of lithium metal and make it more stable.For the lithiophobic carbon fiber cloth(CC),we modified three-dimensional carbon fiber cloth with good conductive nitrogen-doped zinc oxide(N-Zn O/CC),and then prepared a carbon-based composite lithium-metal anode(N-Zn O/CC@Li)by rapid adsorption of molten lithium in 4 seconds.The charge transfer impedance of this composite lithium metal anode is only 24Ω,and it can operate stably at a polarization voltage of 11 m V for over 3000 hours at 1 m A/cm~2 and 1 m Ah/cm~2,and its nucleation overpotential is only 11.73 m V.However,the symmetrical cells with the simple Zn O decorated carbon fiber cloth to infuse molten lithium composite anode(Zn O/CC@Li),only can stable cycle less 400 hours.Moreover,when matched with lithium iron phosphate(LFP)cathode,the capacity retention rate of the N-Zn O/CC@Li|LFP full battery was 93.03%after 100 cycles at 0.2C.Furthermore,the lithium-silicon alloy(Li22Si5)is formed by adding 3 wt%silicon powder as the second phase into the molten lithium for improving the practical application of composite lithium anodes.Then the composite anode(N-Zn O/CC@Li-Si3 wt%)was obtained by N-Zn O/CC infusing the Li-Si3 wt%alloy.The charge transfer impedance of the assembled symmetric cell of N-Zn O/CC@Li-Si3 wt%anode is only 0.4Ω,which is an order of magnitude lower than that of the adsorbed pure lithium metal,and it can run stably at a polarization voltage of 15 m V for more than 900 hours at 3 m A/cm~2 and 1 m Ah/cm~2.After the limit current test,N-Zn O/CC@Li-Si3 wt%composite anode still cycle stalely under the current density reach 10 m A/cm~2 and the area capacity of 10 m Ah/cm~2.When the full battery is assembled with LFP for rate test,the discharge capacity still maintained high level at 20C with 39.4 m Ah/g,which is nearly twice as high as that of pure lithium metal.When matched with commercial LFP cathode(Area load mass≈14 mg/cm~2),the discharge specific capacity still maintained at 98.4m Ah/g after 150 cycles at the rate of 0.5C,and the capacity retention rate is 66.96%,which is nearly 8 times longer than that of pure lithium anode.In summary,the modification of carbon fiber cloth with nitrogen-doped Zn O can effectively improve its lithiophilicity,and the good conductivity of nitrogen-doped Zn O can significantly reduce the charge transfer impedance of the composite lithium metal anode.This strategy of constructing a good conductive lithiophilic three-dimensional skeleton can provide a stable structure for the host-free lithium metal.That can not only achieve the homogeneous deposition of the lithium metal and inhibit the growth of lithium dendrites,but also effectively prevent the volume expansion and structural collapse of the lithium metal.Further,by modifying the chemical composition of the lithium metal,introducing a trace amount of silicon as the second phase,to form a Li-Si alloy with good fluidity.Then it will form a synergistic effect by infusing Li-Si alloy into the lithiophilic carbon fiber cloth(N-Zn O/CC).And to verify the good potential for practical application of the Li-Si alloy composite three-dimensional lithium anode(N-Zn O/CC@Li-Si),we finally matching the LFP cathode with different area mass to prove it.Above all,this research strategy provides an effective idea for the practical research of lithium metal.更多还原