Dolphijn Guillaume, Gauthy Fernand, Vlad Alexandru, Gohy Jean-François
Institute of Condensed Matter and Nanosciences (IMCN), Université Catholique de Louvain, Place L. Pasteur 1, B-1348 Louvain-la-Neuve, Belgium.
Solvay S.A., R&I Solid State Battery Applicability (SSBA) Laboratory, Rue de Ransbeek 310, 1000 Brussels, Belgium.
Polymers (Basel). 2021 Mar 23;13(6):986. doi: 10.3390/polym13060986.
Lithium-ion batteries are today among the most efficient devices for electrochemical energy storage. However, an improvement of their performance is required to address the challenges of modern grid management, portable technology, and electric mobility. One of the most important limitations to solve is the slow kinetics of redox reactions associated to inorganic cathodic materials, directly impacting on the charging time and the power characteristics of the cells. In sharp contrast, redox polymers such as poly(2,2,6,6-tetramethyl-1-piperidinyloxy methacrylate) (PTMA) exhibit fast redox reaction kinetics and pseudocapacitors characteristics. In this contribution, we have hybridized high energy Li(NiMnCo)O mixed oxides (NMC) with PTMA. In this hybrid cathode configuration, the higher voltage NMC (ca. 3.7 V vs. Li/Li) is able to transfer its energy to the lower voltage PTMA (3.6 V vs. Li/Li) improving the discharge power performances and allowing high power cathodes to be obtained. However, the NMC-PTMA hybrid cathodes show an important capacity fading. Our investigations indicate the presence of an interface degradation reaction between NMC and PTMA transforming NMC into an electrochemically dead material. Moreover, the aqueous process used here to prepare the cathode is also shown to enable the degradation of NMC. Indeed, once NMC is immersed in water, alkaline surface species dissolve, increasing the pH of the slurry, and corroding the aluminum current collector. Additionally, the NMC surface is altered due to delithiation which enables the interface degradation reaction to take place. This reaction by surface passivation of NMC particles did not succeed in preventing the interfacial degradation. Degradation was, however, notably decreased when Li(NiMnCo)O NMC was used and even further when alumina-coated Li(NiMnCo)O NMC was considered. For the latter at a 20C discharge rate, the hybrids presented higher power performances compared to the single constituents, clearly emphasizing the benefits of the hybrid cathode concept.
锂离子电池是当今电化学储能效率最高的装置之一。然而，为应对现代电网管理、便携式技术和电动交通等挑战，需要提高其性能。要解决的最重要限制之一是与无机阴极材料相关的氧化还原反应动力学缓慢，这直接影响电池的充电时间和功率特性。与之形成鲜明对比的是，氧化还原聚合物如聚（甲基丙烯酸2,2,6,6 - 四甲基 - 1 - 哌啶氧基酯）（PTMA）表现出快速的氧化还原反应动力学和赝电容特性。在本论文中，我们将高能量的Li（NiMnCo）O混合氧化物（NMC）与PTMA进行了复合。在这种混合阴极配置中，较高电压的NMC（相对于Li/Li约为3.7 V）能够将其能量转移到较低电压的PTMA（相对于Li/Li为3.6 V），从而改善放电功率性能并获得高功率阴极。然而，NMC - PTMA混合阴极显示出重要的容量衰减。我们的研究表明，NMC和PTMA之间存在界面降解反应，将NMC转化为电化学惰性材料。此外，这里用于制备阴极的水相过程也被证明会导致NMC降解。实际上，一旦NMC浸入水中，碱性表面物种溶解，增加了浆料的pH值，并腐蚀铝集流体。此外，NMC表面因脱锂而改变，这使得界面降解反应能够发生。通过NMC颗粒表面钝化的这种反应未能成功防止界面降解。然而，当使用Li（NiMnCo）O NMC时，降解明显减少，而当考虑使用氧化铝涂层的Li（NiMnCo）O NMC时，降解进一步减少。对于后者，在20C放电速率下，与单一成分相比，复合材料表现出更高的功率性能，清楚地强调了混合阴极概念的优势。
