Chen Lin, Dilena Enrico, Paolella Andrea, Bertoni Giovanni, Ansaldo Alberto, Colombo Massimo, Marras Sergio, Scrosati Bruno, Manna Liberato, Monaco Simone
IREQ - Institut de Recherche d'Hydro-Québec , 1800 Boulevard Lionel Boulet, Varennes, QC J3X 1S, Canada.
IMEM-CNR , Parco Area delle Scienze 37/A, 43124 Parma, Italy.
ACS Appl Mater Interfaces. 2016 Feb 17;8(6):4069-75. doi: 10.1021/acsami.5b11632. Epub 2016 Feb 3.
LiMnPO4 is an attractive cathode material for the next-generation high power Li-ion batteries, due to its high theoretical specific capacity (170 mA h g(-1)) and working voltage (4.1 V vs Li(+)/Li). However, two main drawbacks prevent the practical use of LiMnPO4: its low electronic conductivity and the limited lithium diffusion rate, which are responsible for the poor rate capability of the cathode. The electronic resistance is usually lowered by coating the particles with carbon, while the use of nanosize particles can alleviate the issues associated with poor ionic conductivity. It is therefore of primary importance to develop a synthetic route to LiMnPO4 nanocrystals (NCs) with controlled size and coated with a highly conductive carbon layer. We report here an effective surface etching process (using LiPF6) on colloidally synthesized LiMnPO4 NCs that makes the NCs dispersible in the aqueous glucose solution used as carbon source for the carbon coating step. Also, it is likely that the improved exposure of the NC surface to glucose facilitates the formation of a conductive carbon layer that is in intimate contact with the inorganic core, resulting in a high electronic conductivity of the electrode, as observed by us. The carbon coated etched LiMnPO4-based electrode exhibited a specific capacity of 118 mA h g(-1) at 1C, with a stable cycling performance and a capacity retention of 92% after 120 cycles at different C-rates. The delivered capacities were higher than those of electrodes based on not etched carbon coated NCs, which never exceeded 30 mA h g(-1). The rate capability here reported for the carbon coated etched LiMnPO4 nanocrystals represents an important result, taking into account that in the electrode formulation 80% wt is made of the active material and the adopted charge protocol is based on reasonable fast charge times.
磷酸锰锂是下一代高功率锂离子电池极具吸引力的正极材料，因其具有较高的理论比容量（170 mA h g⁻¹）和工作电压（相对于Li⁺/Li为4.1 V）。然而，两个主要缺点阻碍了磷酸锰锂的实际应用：其电子电导率低以及锂扩散速率有限，这导致了正极的倍率性能较差。通常通过用碳包覆颗粒来降低电子电阻，而使用纳米尺寸的颗粒可以缓解与离子电导率差相关的问题。因此，开发一种合成路线来制备尺寸可控且包覆有高导电碳层的磷酸锰锂纳米晶体（NCs）至关重要。我们在此报告了一种对胶体合成的磷酸锰锂NCs进行有效表面蚀刻的工艺（使用LiPF₆），该工艺使NCs可分散在用作碳包覆步骤碳源的葡萄糖水溶液中。此外，NC表面与葡萄糖接触的改善可能有助于形成与无机核心紧密接触的导电碳层，正如我们所观察到的，这导致电极具有高电子电导率。碳包覆蚀刻的磷酸锰锂基电极在1C时的比容量为118 mA h g⁻¹，具有稳定的循环性能，在不同C倍率下循环120次后容量保持率为92%。所提供的容量高于基于未蚀刻的碳包覆NCs的电极，后者从未超过30 mA h g⁻¹。考虑到电极配方中80% wt由活性材料制成且采用的充电方案基于合理的快速充电时间，这里报道的碳包覆蚀刻的磷酸锰锂纳米晶体的倍率性能是一个重要成果。
