钠离子电池负极：现状和未来趋势

锂离子电池在电动汽车和手持电子设备的储能模块中发挥了重要作用。然而，在未来可再生能源发电储能领域中的应用，锂离子电池却因为有限的锂资源和较高的储能成本而受到限制。由于钠在地壳中有更高的丰度，钠离子电池有类似锂离子电池的工作机制，钠离子电池被认为是锂离子电池在可再生能源发电储能应用中的替代者。本文综述了钠离子电池负极近年来在电极材料设计、电化学性能和储钠机制等方面的研究进展。此外，本文还分析了钠离子电池研究、开发和产业化方面存在的迫切需要解决的问题、挑战和未来的发展趋势。

Sodium-ion battery anodes: Status and future trends

Wenli Zhang, FanZhang, Fangwang Ming, and Husam N. Alshareef

EneryChem, 2019, 1(2), 100012.

DOI: 10.1016/j.enchem.2019.100012

Scheme 1. A brief timeline of the development of SIB anodes onkey milestones.

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研究背景：

钠的标准电位（-2.71 V）只比锂（-3.04 V）高大约330 mV，这使得高压钠离子电池的开发成为可能。然而，钠离子（1.02 Å）的半径比锂离子（0.76 Å）的半径大。因此，寻找合适的钠离子宿主负极材料比锂离子电池负极材料更为困难。石墨是最成熟的锂离子电池负极材料。Fouletier等人证实石墨用作钠离子电池负极时，在碳酸酯类电解液中，钠离子只能嵌入石墨生成8阶的NaC₆₄化合物。2001年，Dahn等人最早证实硬炭可以用作钠离子电池的负极（容量约300 mAhg^-1）。近十年来，钠离子电池负极材料发展迅速，研究人员开发了一系列的硬炭、杂原子掺杂碳材料、插层化合物、转化和合金化负极（Figure1）。本文综述了上述材料近年来的最新进展。另外，本文对近年来受到广泛关注的二维层状MXene材料负极和有机材料负极进行了分析综述。

Figure 1. (a) A summary of elements and materials that are potential anodes of SIBs. (b) Some typical anodes along with their working potential range and capacity.

内容简介：

本文首先回顾了可以用于钠离子电池负极的反应机制。然后，针对每一种（类）负极材料，本文讨论了其反应机理、电极材料的设计、电极/电解质界面的调控和实际性能。最后，本文对钠离子电池负极的发展和和产业化需求做了总结和展望。

1. 碳材料负极

Figure 2. Nitrogen doped graphene as high-performance SIB anode.

硬炭可以用作钠离子电池负极。由于其具有较低的成本、较高的首次库伦效率和较好的稳定性，硬炭成为钠离子电池负极的首选。本文从硬炭的结构、杂原子掺杂和界面调控入手，系统综述了提高硬炭容量和首次库伦效率的方法。类石墨烯类材料（Figure 2）可以在制备过程中掺杂高浓度的杂原子，使其具有较高的容量。此外，石墨化材料可以通过调整层间距，调控电极/电解质界面等方法提高其性能。石墨烯和膨胀石墨，可以打破石墨在碳酸酯类电解质中不能嵌钠的局限。通过调节电极/电解质界面，利用醚类电解质，钠离子可以实现钠离子与溶剂分子共嵌入到石墨层间，本文对以上相关研究进行了详细的综述和讨论。

2. 转化和合金化负极

Figure 3. Micron-sized Bi metal particles as high-performance SIB anode.

转化和合金化负极，由于具有较高的容量，而受到广泛的关注。但是此类电极材料，往往在嵌钠和脱钠过程中有粉化和体积膨胀的问题。电极结构的纳米化、复合化设计可以保证此类电极具有更好的稳定性。但是，纳米化导致电极材料首次库伦效率和体积容量降低的问题值得注意。此类电极材料通过电极/电解质界面的调控（Figure 3）和粘结剂的优化可以获得优异的循环稳定性。

3. 钠金属负极和MXene负极

Figure 4. Mechanism study of sodiation of MXene.

金属钠由于具有很低的电位和较高的容量而受到广泛的关注。与锂金属负极类似，钠金属负极在充放电过程中存在体积膨胀和枝晶生长的问题。本文概述了几类金属钠负极保护的方法。此外，本文也提出了钠金属负极研究中存在的问题。MXene是近年来能源储存和转化领域的热点材料。MXene作为钠离子电池负极材料的一大缺陷是容量低。本文重点回顾了MXene在储钠过程中的结构变化和储钠机理（Figure 4）。此外，本文概述了MXene在结构改进和其衍生物用于钠离子电池负极的进展。

4. 有机物负极

Figure 5. Organic anodes for SIB.

有机负极是最早开发用于钠离子电池的负极材料之一。不同有机负极表现出截然不同的性能和活性位点。本文概述了有机负极的发展和近年来的最新进展。同时，本文对高容量钠离子电池负极作了展望。

总结与展望：

受限于钠离子电池材料较低的容量，当前钠离子电池的实际能量密度较低，这导致其性价比相对于锂离子电池并不明显。开发合适的高容量的负极还是当前的主要研究方向。硬炭材料具有相对较高的容量，和较高的振实密度。而且，硬炭材料的首次库伦效率较高，这使得其成为最适合钠离子电池的负极材料。氮掺杂的无定形炭虽然具有较高的容量、但是其较低的振实密度和较高的充放电电压使其可实用性相对硬炭材料并不明显。

转化和合金化负极虽然具有较高的容量，但是其性能往往受到体积膨胀和材料粉化局限。纳米工程可以制备高性能的转化和合金化负极，此类高性能负极需要开发高通量的制备技术。受限于MXene 较低的容量和较高的制备成本，当前，MXene不适合用作钠离子电池的负极材料。MXene作为一种功能性的添加剂或者基体材料适合用于制备高性能钠离子电池负极，而有机负极的制备和其稳定性是其应用过程中的障碍。

本综述回顾了近年来钠离子电池负极在储能机制、结构设计和构效关系等方面的研究进展。此外，本文还展望了钠离子电池研究、开发和产业化方面存在的迫切需要解决的问题、挑战和未来的发展趋势。

作者简介：

WenLi Zhang is now a post-doctoral fellow in Prof. Husam Alshareef's group at King Abdullah University of Science andTechnology (KAUST), Saudi Arabia. Under the supervision of Prof. Haibo Lin, he obtained his B. Eng. from Jilin University, China, in 2011; and Ph.D. in Physical Chemistry from Jilin University, China, in 2017. Currently, hisresearch interests focus on carbonaceous materials for supercapacitor, and rechargeable batteries, such as lead-acid battery, and (lithium/sodium/potassium)-ion batteries.

Fan Zhang is now a Ph.D. student under the supervision of professor Husam N. Alshareef at the King Abdullah University of Science and Technology (KAUST). He completed his undergraduate studies at the Shandong University (2014), followed by a master degree in Materials Science from KAUST in 2017. His main research is focused on synthesis and characterization of 2D materials and their applications as electrodes for lithium, and sodium ion batteries.

Fangwang Ming received his master degree in chemical engineering in 2017 from Xiamen University. He is currently a Ph.D student under the supervision of Professor Husam N. Alshareef at King Abdullah University of Science & Technology (KAUST). His research interest relates to functional nanomaterials, especially 2D materials, for efficient energy storageand conversion.

Husam Alshareef is a Processor of Materials Science and Engineering at King Abdullah University of Science and Technology(KAUST). He obtained his Ph.D. at North Carolina State University, Raleigh,USA. He then did his post-doctoral work at Sandia National Laboratory, USA. Following ten years in the semiconductor industry, he joined KAUST in 2009, where he has been running a research group focused on developing inorganic nanomaterials for energy and electronics. He is the author of 480 articles, he has nearly 80 issued patents, and over 200 international invited &contributed presentations. He has won numerous awards including the UNDP Undergraduate Fellowship, Seth Sprague Physics Award, North Carolina State University Dean’s Fellowship, U.S. Department of Education Electronic Materials Fellowship, Sandia National Laboratory post-doctoral Fellowship, the SEMATECHC orporate Excellence Award (2006), two DOW Sustainability Awards with his students in (2011) and (2014),  the AH Shoman Award for Excellence in Energy Research (2016), the KAUST Distinguished Teaching Award (2018), and the Kuwiat Prize in Clean and Sustainable Technologies (2018). He is the Fellow of the Royal Society of Chemistry,  Fellow of the American Physical Society, IEEE Distinguished Speaker in Nanotechnology, and Senior Member of IEEE. He was Chair of the 2014 Materials Research Society (MRS) Fall Meeting in Boston, USA, and has served on various MRS committees. He established the first MRS Student Chapter outside USA at KAUST. He is on the Editorial Board of Wiley's Small Methods, and Elsevier's EnergyChem. He is a highly cited researcher in Materials Science by Clarivate Analytics (2019). 

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